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Bureau of Mines Information Circular/1988 




Human Factors in Mining 



By Mark S. Sanders and James M. Peay 




UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 9182 



Human Factors in Mining 



By Mark S. Sanders and James M. Peay 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 



ii 






Library of Congress Cataloging-in-Publication Data 



Sanders, Mark S. 

Human factors in mining. 

(Information circular/United States Department of the Interior, Bureau of Mines; 9182) 
Includes bibliographies. 
Supt. of Docs. No.: I 28.27 

1. Mining engineering— Safety measures. 2. Human engineering. I. Peay, James M. II. 
Title. III. Series: Information circular (United States. Bureau of Mines) ; 9182. 



TN295.U4 



622 s 



622 '.8 



87-600304 



CONTENTS 



Abstract 1 

Chapter 1.— Introduction 2 

Definition of human factors 2 

Basic model 3 

What human factors is not 3 

Road blocks to the application of human 

factors 3 

History of human factors 4 

1940-50— war years -. 4 

1950-60— birth of a profession 4 

1960-80— recognition and expansion 4 

1980— a household word 4 

History of human factors in mining 4 

1870-1950— early mechanization 5 

1950-70— modern mechanization and the 

coal act 6 

1970— birth and growth of human factors 

in mining 6 

Coverage r*. 7 

References 7 

Chapter 2.— Human factors in the design 

of systems 9 

Characteristics of systems 9 

Systems have a purpose 9 

Systems are hierarchical 10 

Systems operate in an environment 10 

Components serve functions 11 

Components interact 11 

Systems, subsystems, and components have 

inputs and outputs 11 

How engineers really design 11 

Stages in the design of systems 12 

Stage 1: determine objectives and system 

specifications : 12 

Stage 2: define the system 12 

Stage 3;- basic design 12 

Stage 4: interface design . 16 

Stage 5> facilitator design 18 

Stage 6: testing 18 

Discussion 18 

References 18 

Chapter 3.— Human capabilities and limitations . . 19 

Who are miners 19 

Human as an information receiver 20 

Sight 20 

Accommodation 20 

Adaptation 20 

Field of vision 20 

Visual acuity 21 

Detection of movement 21 

Hearing 22 

Sound localization 22 

Tone and loudness discrimination 23 

Masking . .- 23 

Effect of age on hearing 23 

Smell , 23 

Human as information processor 23 

Memory. 23 

Decisionmaking 24 

Attention 25 



Page 

Human as action taker 26 

Reaction time 26 

Stimulus reception time 26 

Processing time 26 

Response selection time 26 

Movement time 27 

Movement accuracy 27 

Positioning movements 27 

Continuous movements 27 

Repetitive movements 27 

Anatomical characteristics 27 

Percentiles 27 

Fallacy of the "average" person 27 

Other limitations of anthropometric data 28 

Static anthropometric data 28 

Range of movement 28 

Reach envelopes 28 

Strength 29 

Endurance 30 

Circadian rhythms 30 

Physiological adjustment 31 

Shift work 32 

Discussion 32 

References 32 

Chapter 4.— Human error and accidents 34 

Human error 34 

Broad classification of human error 35 

Action classification of human error 35 

Information-processing model of human 

error 35 

Warning-hazard classification of human 

error 35 

What is an accident 36 

Human error and accidents 36 

Theories of accident causation 38 

Accident proneness theories 38 

Job demand versus worker capability 

theories 39 

Psychosocial theories 40 

Injury statistics 40 

Industrywide comparisons 40 

Comparisons with European countries 42 

Costs of accidents 42 

Discussion 44 

References 44 

Chapter 5.— Information displays 45 

Choosing a display 45 

Visual displays 46 

Quantitative displays 46 

Design features of quantitative displays .... 47 

Scale markers 47 

Numerical progression of scales 48 

Design of pointers 48 

Relative importance of design features 48 

Qualitative displays 48 

Signals and warning lights 49 

Signs and labels 50 

Typography 50 

Pictorial signs and labels 51 



CONTENTS— Continued 



Page 

Auditory displays 51 

Alarms 51 

Speech 52 

Intensity of speech 52 

Intelligibility of speech 52 

Preferred octave speech interface level 

(PSIL) 53 

Hearing protection and speech 53 

Underground loudspeaker system: a case 

study 53 

Problems during introduction of the 

system 53 

Results of installation 54 

Olfactory displays 54 

Discussion 54 

References 54 

Chapter 6.— Design of controls, equipment, 

and tools 55 

Controls 55 

Types of controls 55 

Factors in control design 56 

Identification of controls 56 

Control-response ratio 59 

Resistance 59 

Deadspace 59 

Backlash 59 

Design of specific controls 59 

Equipment design 60 

Compatibility 60 

Conceptual compatibility 60 

Movement compatibility 60 

Spatial compatibility 61 

Placement of displays and controls 61 

Arrangement of controls and displays 61 

Standardization 61 

Location of controls and displays 63 

Special problems in equipment design 66 

Seating for low-seam coal equipment 

operators 66 

Operator field of vision 70 

Egress-ingress on surface mining 

equipment 72 

Designing for maintainability 77 

Handtool design 78 

Principles of handtool design 79 

Maintain a straight wrist 79 

Avoid tissue compression stress 79 

Avoid repetitive finger action 79 

Design for safe operation 79 

Women and left-handers 79 

Vibration-induced white finger 79 

Discussion 80 

References 80 

Chapter 7.— Physical work 82 

Work physiology 82 

Muscle 82 

Energy consumption 83 

Cardiac output and aerobic capacity 83 

Measurement of work 84 



Page 

Energy expenditure at work 86 

Grades of physical work 86 

Energy expenditures for common mining 

tasks 86 

Recommended energy expenditure levels 88 

Manual materials handling 90 

Materials handling accidents 91 

Biomechanics of lifting 91 

Effects of lifting posture 93 

NIOSH recommended lifting load limits 94 

Reducing the risk 95 

Redesign the task 95 

Redesign the workplace 95 

Selection of workers 96 

Training workers 96 

Discussion 97 

References 97 

Chapter 8.— Environmental factors 99 

Illumination 99 

Measurement of light .' 99 

Luminous flux 100 

Illuminance 100 

Luminous intensity and luminance 100 

Reflectance 100 

Contrast 100 

Illuminance and performance 100 

Illumination requirements 101 

Glare 102 

Noise 102 

Measurement of noise 102 

Frequency 103 

Intensity 103 

Indexes of noise intensity 103 

Conditions in mining 103 

Standards for noise exposure in mining 104 

Hearing loss 104 

Other physiological effects of noise 104 

Effects of noise on performance 105 

Controlling the noise problem 105 

Hearing protection 107 

Whole-body vibration 108 

Vibration terminology 108 

Effects of vibration on humans 108 

Health effects 108 

Performance effects 108 

Vibration exposure standards 108 

Vibration exposure of surface coal miners .... 109 

Controlling vibration 109 

Heat stress 109 

Physiological response to heat stress 109 

Indexes of head stress 110 

Effective temperature (ET) 110 

Wet-bulb-globe temperature (WBGT) Ill 

Heat stress index (HSI) Ill 

Heat stress conditions in mining Ill 

Performance effects of heat stress Ill 

How much is too much 112 

Protection from heat stress 112 



Ill 



CONTENTS— Continued 



Page 

Cold stress 113 

Frostbite 113 

Performance effects of cold 113 

Protection from cold stress 114 

Discussion 114 

References 114 

Chapter 9.-Training 116 

Effectiveness of training 116 

Training: what is required 117 

Training requirements in the United States . . 117 

Training requirements in other countries 117 

Discussion 118 

Training practices in the United States 118 

Characteristics of successful safety programs ... 119 

Management 119 

Training and incentives 119 

Accident reduction 119 

Basic concepts in human learning 120 

Learning versus performance 120 

Performance feedback 120 

Reward and punishment 121 

Learning from models and examples 121 

Methods of training 122 

Classroom training 122 

Part-task simulation 122 

Full-task simulation 122 

Simulated mine environments 122 

Training sections in an actual mine 123 

On-the-job training 123 

Developing a training program 124 

Assess training needs 124 

Write goals and objectives 125 

Determine criteria and evaluation 

measures 125 

Select training modes and media 125 

Develop training materials 125 

Evaluate effectiveness 126 

Revise 126 

Safety awareness programs 126 

Consol's program 126 

Elements of a successful program 126 

Safety signs 126 

Discussion 127 

References 127 

Chapter 10.— Motivation and organizational 

development 128 

Motivation 128 

Motivation and performance 128 

Motivation and needs 129 



Page 

A theory of motivation 129 

Valence 129 

Effort-performance (E-P) expectancy 129 

Performance-outcome (P-O) expectancy 129 

The model 129 

Implications of the model 130 

Organizational climate 131 

Organizational development 131 

Rushton autonomous work group 

experiment 132 

Background 132 

Autonomous work groups 132 

Results 132 

Hecla team-building project 132 

Background 132 

Team building 133 

Performance appraisal system 133 

Safety activities 133 

Supervisory skills training 133 

Results 134 

Cost 134 

Texasgulf management training study 134 

Background 134 

Objective supervisory performance 

appraisal 134 

Leadership training 135 

Supervisory skills training 135 

Institutionalization 135 

Results 135 

Cost 135 

Quality control circles 135 

QC circles at the Captain Mine 136 

Results 136 

Discussion 136 

References 136 

Appendix A.— Static anthropometric data for 

male and female military personnel 138 

Appendix B.— Typical joint mobility data 
showing 5th and 95th percentile male and 

female limits 141 

Appendix C— Examples of pictorial safety signs 

recommended for use in the mining industry . . . 142 
Appendix D.— Summary of selected data regarding 

design recommendations for control devices .... 145 
Appendix E.— Selected data on access space 

required to perform maintenance tasks 146 



IV 



ILLUSTRATIONS 

Page 

1-1. Basic human-hardware-environment system 3 

1-2. Undercutting a coal face before mechanization 5 

1-3. Early Harrison Pick cutting machine 5 

1-4. Use of animals for hauling coal 6 

2-1. Schematic diagram of haulage vehicle subsystem within the total mine system 10 

2-2. Schematic diagram of inputs and outputs between subsystems of a system 11 

2-3. Stages in the development of a system 12 

2-4. Example of a column format used in task analysis 13 

2-5. Example of an operational sequence diagram (OSD) used in task analysis 14 

2-6. Example of a timeline used in task analysis 15 

2-7. Graphic illustration of the results of a link analysis of a roof bolting operation 16 

2-8. Example of an articulated plastic manikin for evaluation of engineering drawings 16 

2-9. Three-dimensional manikin produced by CAP based on external anthropometric measurement inputs . . 17 

3-1. Diagram of the eye 20 

3-2. Field of vision and effect of eye and head rotation 21 

3-3. Illustration of the concept of visual angle 21 

3-4. Effect of caplamp and background illumination on detection of moving objects in the periphery 

of the visual field 21 

3-5. Illustration of principal structures of the ear 22 

3-6. Illustration of the cochlea 22 

3-7. Changes in hearing sensitivity with age for 1,320 underground coal miners 23 

3-8. The load-haul-dump-return cycle in surface mining creates a situation highly conducive to lapse 

in attention and alertness 25 

3-9. Reaction time as a function of the number of response choices available 26 

3-10. Arm reach envelope for movements using a number of hand-grasp positions in three-dimensional space 29 

3-11. Foot reach envelopes for various types of pedal operations 29 

3-12. Arm strength data 30 

3-13. Maximum force exerted on a foot pedal and maximum torque applied to a 22-in-diameter steering 

wheel by truck drivers 31 

3-14. Endurance time as a function of the force maintained 31 

3-15. Typical circadian rhythm for body temperature 31 

4-1. One consequence of operator error 37 

4-2. Relationship between age and disabling injury rate 38 

4-3. Supervisor fatalities in coal mining as a function of experience at mine, experience in job 

classification, and total mining experience 39 

4-4. Percent of fatalities, nonfatal-days-lost, and no-days-lost injuries occurring in 1983 for each of the 

major segments of the mining industry 41 

4-5. Nonfatal-days-lost and no-days-lost injury rates for 1983 for each of the major segments of the 

mining industry 41 

4-6. Comparison of nonfatal-days-lost injuries from major accident categories for the major segments of 

the mining industry in 1983 41 

4-7. Fatality rate per 200,000 employee-hours for U.S. underground coal mines from 1931 through 1983 ... 42 

4-8. Comparison of fatality data between U.S. and European underground coal mines 42 

4-9. Average cost of a fatality in the mining industry, 1975-81 43 

4-10. Average cost of a disabling injury in the mining industry, 1975-81 43 

4-11. Example of characteristic effect of a fatal injury on production in an underground mine 44 

5-1. Examples of quantitative displays 46 

5-2. Illustration of several numeric scale concepts 47 

5-3. Recommended format for quantitative scales under normal and low illumination conditions 47 

5-4. Illustrations of coding methods for marking zones of instruments that are to be read qualitatively .... 48 

5-5. Mean response time for detecting pointer in danger zone for three dial designs 49 

5-6. Two patterns of dials used in a check-reading experiment 49 

5-7. Definition of stroke width to height and width to height ratios for alphanumeric characters 50 

5-8. Illustrations of stroke width to height ratios of letters and numerals 50 

5-9. Examples of pictorial signs that caused confusion among mining industry employees 51 

6-1. Common types of controls classified by type of information they transmit most effectively 56 

6-2. Control station of a low-seam coal auger 57 

6-3. Controls with different length lever controls 57 

6-4. Example of operator-provided shape coding 58 

6-5. Control knob shapes that are easily identified by touch while wearing gloves 58 

6-6. Control shapes recommended for underground roof bolters 59 

6-7. Movement compatibility relationships where dial and display are in same plane 60 



ILLUSTRATIONS— Continued 

Page 

6-8. Compatible control-display movements when controls and displays are in different planes 61 

6-9. Common meanings of lever movements 61 

6-10. Examples of spatial compatibility between a bank of controls and displays 61 

6-11. Different arrangements of roof bolter controls from one manufacturer 62 

6-12. Brake, clutch, and throttle control placement on eight 120-st-capacity and smaller haulage trucks 62 

6-13. Location of service brake relative to steering wheel on four front-end loaders 62 

6-14. Preferred vertical surface areas and limits for various types of control functions operated by a 

seated operator 63 

6-15. Recommended dimensions and layout of seated operator workstations 64 

6-16. Recommended configurations of a vehicle cab 65 

6-17. SAE J898a recommended practice for control locations for construction and industrial equipment 

design 66 

6-18. Recommended layout of a standing operator workstation 67 

6-19. Recommended separation between adjacent controls for one- and two-hand operation 67 

6-20. Examples of typical seating postures in low-seam coal mining equipment 68 

6-21. Seating space envelopes for 95th percentile male and 5th percentile female operators in two cab 

heights 69 

6-22. Relationship between interior cab height and required interior cab length needed to accommodate 

various sized people 70 

6-23. Human-factored seat for low-seam mining equipment 70 

6-24. Illustration of front and side visual limitations from the cab of a 150-st-capacity rear-dump haulage 

truck 71 

6-25. Plan view illustrating front and side visual limitations and blind areas from the cab of a 

150-st-capacity rear-dump haulage truck 71 

6-26. Typical installation of an improved visibility system for large haulage trucks 71 

6-27. Fresnel lens blind area viewer used to enhance visual field of haulage truck oeprators 72 

6-28. Improved field of view resulting from installation of system shown in figure 6-27 72 

6-29. Plan view of visual attention locations identified for continuous miner operators 72 

6-30. Human eye reference measurement instrument used to assess fields of visibility from operators' cabs . . 73 

6-31. Excessively flexible lower section support on haulage truck ladder 74 

6-32. Inappropriate height of first step of haulage truck ladder 74 

6-33. Design recommendations for stairs and ladders 75 

6-34. Stairs used on haulage trucks 76 

6-35. Schematic diagram showing relationship of seat, steering wheel, and doorway on a typical tractor .... 77 

6-36. Example of a well-designed access door 77 

6-37. Concept of Bureau-sponsored four-spring-supported lower steps for large haulage trucks 77 

6-38. Bureau-sponsored four-spring-supported lower steps colliding with a large rock 77 

6-39. Bureau-sponsored hydraulic "power" step for egress and ingress from tractors, dozers, and shovels .... 78 

6-40. Examples of common handtools designed to permit users to maintain straight wrists 79 

7-1. Electromyogram recording of biceps muscle during static force application 83 

7-2. Schematic representation of metabolic process that takes place during muscular work 83 

7-3. Oxygen uptake during muscular work 84 

7-4. Aerobic capacity of male miners by age group 84 

7-5. Linear relationship between heart rate and oxygen uptake for six adult males 85 

7-6. Underground worker hanging brattice cloth 85 

7-7. Effect of weight of objects being lifted and lift posture on energy expenditure 87 

7-8. Effect of work pace on energy expenditure for a lifting task 87 

7-9. Energy efficiency of lifting various weights from different starting positions 87 

7-10. Energy expenditure and activity profile for roof bolter helper 88 

7-11. Recommended maximum work times for males and females performing tasks at various levels 

of energy expenditure 89 

7-12. Materials handling accidents by major activity or function 92 

7-13. Illustration of basic muscle biomechanics and lever analog 92 

7-14. Diagram of spinal column 93 

7-15. Calculated lower-back muscle force and compressive forces acting on the L 5 -S! disk resulting from 

lifting a timber post 93 

7-16. Cutaway view of a ruptured L 5 -Sj disk pressing the spinal nerve 93 

7-17. Comparison of lower-back compression forces associated with stoop-back and squat methods of 

lifting a wide object .- 94 

7-18. Incidence and severity of back injury as a function of the job severity index 96 

8-1. Effect of adding additional background luminance on the speed of detecting holes in a floor at a 

distance of 10 ft 101 



VI 



ILLUSTRATIONS— Continued 

Page 

8-2. Sine wave sound pressure wave showing one cycle with corresponding changes in air pressure 103 

8-3. Relative response characteristics of the A, B, and C sound-level meter scales and the human ear 

at threshold 103 

8-4. Typical noise levels of machinery in underground and surface mining 104 

8-5. Hearing loss among underground coal miners, by age 104 

8-6. Example of type of information contained in Mining Machinery Noise Control Guidelines 106 

8-7. Typical noise-time histories in passenger and operator compartments of an untreated and noise- 
reduction-treated mantrip 107 

8-8. Vertical vibration exposure limits for the preservation of performance 109 

8-9. Mechanical response of a person's body to vibrations when sitting in different seats 109 

8-10. Time until young, fit, unacclimatized men collapse from exhaustion 110 

8-11. Setup for manually obtaining temperatures used to compute wet-bulb-globe temperature Ill 

8-12. Effects of ambient temperature on miners loading mine cars and drilling rock 112 

8-13. Relationship between rate of unsafe behaviors and wet-bulb-globe temperature 112 

9-1. Results of an experiment that demonstrates effectiveness of performance feedback on incidence 

of safe behaviors 120 

9-2. OBSAC part-task simulator held in instructor's lap in port seat of a haulage vehicle 123 

9-3. Shuttle car training system full-task simulator 123 

9-4. Instructional system design approach to development of training programs 124 

10-1. Schematic representation of expectancy theory of motivation 130 

10-2. Results of organizational development intervention at Lucky Friday Mine 134 

10-3. Incidence rates of lost-time accidents for the Lucky Friday Mine, Star Mine, and other mines in the 

Coeur d'Alene mining district 134 

A-l. Standing body dimensions 138 

A-2. Seated body dimensions 139 

A-3. Body depth and breadth dimensions 140 

B-l. Typical joint mobility data 141 



TABLES 

2-1. Methods of collecting task analysis information 13 

4-1. Information-processing model of human error 35 

4-2. Human error classification of accidents in South African gold mines 36 

4-3. 1982-83 medical compensation costs paid per incident by a major coal company, by type of injury 

sustained 43 

5-1. Average times for qualitative and quantitative reading with three types of scales 48 

5-2. Recommended letter heights for labels and signs for various distance conditions 51 

5-3. Recommended heights of letters on emergency signs 51 

5-4. Characteristics and features of certain types of audio alarms 52 

5-5. Maximum distance between speaker and listener to carry on a satisfactory conversation 53 

6-1. Common types of controls 56 

6-2. Descriptions of common types of control resistance 59 

6-3. Compatible directions of movement associated with various control functions 60 

7-1. Effect of vertical starting position on energy expenditure 86 

7-2. Grade of physical work based on energy expenditure level 86 

7-3. Energy expenditures for four low-seam tasks 86 

7-4. Average energy expenditures for mining tasks in South African gold mines 88 

7-5. Common mine materials and their weights 91 

7-6. Materials handling nonfatal-days-lost injuries in the mining industry, 1983 91 

7-7. Objects involved in overexertion back injuries suffered by underground coal miners during 1981 91 

7-8. Maximum lift frequency based on average vertical location and period of performance 95 

8-1. Examples of average reflectances of rocks and minerals from underground metal and nonmetal mines . 100 

8-2. Samples of illumination standards set by various countries for underground coal mining 101 

8-3. Walsh-Healy noise criteria for underground and surface mining 104 

8-4. Effects of noise control treatments installed on a diesel track dozer 105 

8-5. Advantages and disadvantages of insert-type and muff-type hearing protection devices 107 

8-6. Comparison of proposed WBGT threshold values 112 

8-7. Equivalent temperatures based on windchill index 113 

9-1. Content of underground and surface mine health and safety training, by type 118 



Vll 



TABLES— Continued 

Page 

9-2. Sources of information for assessing training needs 125 

10-1. Factors that influence performance-outcome and effort-performance expectancies 131 

A-l. Standing body dimensions 138 

A-2. Seated body dimensions 139 

A-3. Body depth and breadth dimensions 140 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


°c 


degree Celsius 


kg-m 


kilogram-meter 


c 


candle 


kHz 


kilohertz 


c/in 2 


candle per square inch 


kJ 


kilojoule 


c/m 2 


candle per square meter 


km 


kilometer 


cal 


calorie 


L 


liter 


cal/min 


calorie per minute 


L/min 


liter per minute 


cm 


centimeter 


lb 


pound 


dB 


decibel 


lb-in 


pound-inch 


dBA 


decibel, A-weighted 


lm 


lumen 


deg 


degree 


lm/ft 2 


lumen per square foot 


op 


degree Fahrenheit 


lx 


lux 


fc 


footcandle 


m 


meter 


fL 


footlambert 


m/s 2 


meter per square second 


ft 


foot 


m 2 


square meter 


ft-lb 


foot-pound 


mg 


milligram 


ft/s 2 


foot per square second 


min 


minute 


h 


hour 


mL 


milliliter 


Hz 


hertz 


mL/(kg/min) 


milliliter per kilogram per minute 


in 


in 


mm 


millimeter 


in/oz 


inch per ounce 


M N/m 2 


micronewton per square meter 


in/s 2 


inch per square second 


oz 


ounce 


in 2 


square inch 


psi 


pound (force) per square inch 


J 


joule 


s 


second 


kcal 


kilocalorie 


sr 


steradian 


kcal/h 


kilocalorie per hour 


St 


short ton 


kcal/kg-m 


kilocalorie per kilogram-meter 


W 


watt 


kcal/(m 2 /h) 


kilocalorie per square meter per hour 


yd 


yard 


kcal/min 


kilocalorie per minute 


yr 


year 


kg 


kilogram 







HUMAN FACTORS IN MINING 



By Mark S. Sanders 1 and James M. Peay 2 



ABSTRACT 

There is a growing awareness among mining professionals that the human factor 
plays a significant role in safety and productivity. Since the 1960's, the science of human 
factors, or ergonomics, has been making inroads into the mining industry, and a con- 
siderable amount of research has documented human-factor -related mining problems 
and solutions. This Bureau of Mines report is directed toward summarizing the applica- 
tion of human factors to improving safety, productivity, and the general physical and 
psychological working conditions of miners. 

The aim of this report is to familiarize the readers with the role of human factors 
in the mining industry and the benefits that can accrue by systematically applying 
available human factors principles and data. The text contains 10 chapters dealing with 
human, equipment, and environmental factors. Each chapter builds on the previous 
chapter; therefore, it is recommended that the chapters be read sequentially. However, 
if the report is used as a supplemental text, say in a mining safety course, chapters 
can be assigned in any order to supplement other readings. 



1 Senior staff scientist, Essex Corp., Westlake Village, CA. 

2 Supervisory engineering psychologist, Bureau of Mines, Pittsburgh Research Center, Pittsburgh, PA. 



CHAPTER 1.— INTRODUCTION 




The mining industry has undergone and continues to undergo technological innovation at an increasingly rapid pace. 



It was not too long ago that horses were still in the 
mines, and people loaded ore and coal by hand. In 1950, for 
example, almost one-third of the coal produced underground 
in the United States was loaded by hand {24)} Although 
many jobs still require high levels of physical labor, mech- 
anization has greatly reduced the physical demands placed 
on the mine worker. Today, mines are safer than at any 
period in the past and safety is now an important part of 
mine management. Coupled with the concern for safety is 
management's ever present concern for productivity and 
the resultant economic viability of the mining operation. 

Over the last quarter century or so, there has been a 
growing recognition within industrialized countries that 
people are the key to both safety and productivity. Tech- 
nology has done much to increase productivity and safety 
in the mining industry. It has become obvious, however, 
that as technology advanced, new demands were being 
placed on the worker. More attention, not less, had to be 
paid to how people and technology would work together. 
How could equipment and tasks be designed to match the 
capabilities and limitations of the people who had to operate 
and maintain them? This is one of the questions addressed 
by human factors. The Bureau of Mines launched its human 
factors research program over a decade ago (19), and a con- 
siderable body of knowledge now exists concerning human 
factors in mining. 

The purpose of this report is to introduce the reader to 
human factors and its application in mining, to summarize 
much of the current knowledge, and to illustrate the util- 
ity of considering human factors in the design of equipment, 
tasks, procedures, and environments within the mining 
industry. 

DEFINITION OF HUMAN FACTORS 

Before attempting to define human factors, a word about 
terminology is in order. Unfortunately, several terms are 
used interchangeably to refer to the same scientific dis- 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



cipline. The two leading terms are human factors and 
ergonomics. A third term, human engineering, is somewhat 
dated and seems to be declining in use. The term "human 
factors" is used most often in the United States and Canada. 
Both countries have professional associations that use the 
term in their name (i.e., The Human Factors Society in the 
United States and The Human Factors Association of 
Canada in Canada). In the United States, however, the more 
scientific sounding term "ergonomics" is often used in prod- 
uct advertisements for such things as automobiles, com- 
puter hardware, and chairs. 

In the rest of the world, the term "ergonomics" is pre- 
ferred; and in many countries, including the United 
Kingdom, France, Federal Republic of Germany, Poland, 
Israel, and Mexico, there are ergonomic professional 
organizations. 

Although most authors do not attempt to distinguish 
the two terms, one book does try to make the distinction 
(7). Reference 7 indicates that ergonomics traditionally 
focuses on how work affects people, emphasizing physiolog- 
ical responses to physically demanding work; environmen- 
tal stressors, such as heat, noise, and illumination; complex 
psychomotor assembly tasks; and visual monitoring tasks. 
The goal is chiefly to reduce fatigue by designing tasks 
within people's work capacity. In contrast, reference 7 
argues that human factors traditionally is more interested 
in the human-hardware interaction, focusing on behavior 
of people as they interact with equipment, workplaces, and 
their environment, as well as on human size and strength 
capabilities relevant to equipment and workspace design. 
The goal is chiefly to reduce the potential for human error. 

Although this distinction may be correct in theory, in 
practice there is so much overlap in focus, emphasis, and 
goals that it is safer to consider the two terms synonymous. 
In fact, it should be pointed out that it was the Human Fac- 
tors section at Eastman Kodak that published the book en- 
titled "Ergonomic Design for People at Work" (7X The term 
"human factors" will be used in this report, but human fac- 
tors and ergonomics will be considered synonymous. 

What then is the definition of human factors? The 
simplest definition is that human factors is designing for 



human use. The following is a more elaborate definition that 
most people would find acceptable. Human factors is the 
systematic application of relevant information about human 
characteristics, abilities, expectations, and behaviors to the 
design of machines, tools, facilities, procedures, and envi- 
ronments that people use. The goal of human factors is to 
enhance the operational efficiency, and the health and 
safety of the people using the system. 

BASIC MODEL 

Human factors focuses on the human-hardware- 
environment system. The basic system, one person and one 
machine operating inside an environment, is shown in fig- 
ure 1-1. This, of course, is an oversimplification. Most 
systems involve more than one person and more than one 
piece of hardware, and they operate within a changing en- 
vironment. Systems are more fully discussed in chapter 2, 
but this rudimentary model illustrates the basic elements 
of concern to human factors. The person receives informa- 
tion from the machine by way of displays. These displays 
can be visual, auditory, tactual, and olfactory in nature. The 
human processes the information and makes inputs to the 
machine by way of control devices: push buttons, knobs, joy- 
sticks, steering wheels, etc. The person and machine are 
affected by, and receive information from, the environment. 
The machine affects the environment, often at the direc- 
tion of the person. Although people can directly influence 
the environment, this is usually accomplished through some 
hardware device. 

As an example of this model, consider a worker operat- 
ing a jackleg drill in a hard-rock mine. The person receives 
information from the drill: hydraulic pressure from a gauge, 
vibrations and feel of the drill, visual confirmation of the 
bit penetrating the rock, and the sound of the drill. Based 
on this information and previous experience and knowledge, 
the worker manipulates the controls to successfully drill 
the hole. Drilling the hole alters the environment. It puts 
a hole where none existed before; noise, dust, and mist are 
generated; and perhaps rocks on the floor are moved by the 
support leg of the drill. These aspects of the environment 
affect the worker by reducing visibility, creating new trip- 
ping hazards, or perhaps causing a temporary, partial loss 
of hearing. 





Dust Environment Noise 


c 
o 

a 

c 

I 


3 
O 

a> 

a. 

E 

«2 


, 


i 






Machine 












' 










G 


Displays 

Controls 


s*4 


V 










, 


i 






*■ i luman 


, 






Obstacles Glare People Vibration 



Figure 1-1.— Basic human-hardware-environment system. 



WHAT HUMAN FACTORS IS NOT 

Human factors specialists are concerned with the 
human and the human's interactions with equipment and 
environment. They are concerned with how best to present 
information, configure controls, and design the hardware 
so humans can operate it efficiently, comfortably, and safely. 
They are concerned with how the environment affects 
human performance, and how humans sense and respond 
to the environment. They are interested in the human as 
an information processor, decisionmaker, and energy source 
for physical work. 

These are just some of the concerns human factors 
specialists have regarding the human-hardware-environ- 
ment system. Equally important to the understanding of 
human factors is understanding what human factors is not. 
Unfortunately, when asked what human factors is, many 
engineers, designers, and supervisors often tell what it is 
not. 

Human factors is not just the application of checklists 
and guidelines. Although checklists can be helpful, they do 
not constitute a human factors evaluation. The problem 
with checklists is that they do not deal with interactions 
between items and the tradeoffs that must be made between 
competing criteria. Guidelines are just that, guidelines. Two 
people using the same guidelines can produce vastly dif- 
ferent designs {26). 

Human factors is not using yourself as the model for 
designing things. Just because it makes sense to you, or 
fits your capabilities, is absolutely no guarantee that it will 
make sense to, or fit, the people who will ultimately use 
it. There is considerable information available to assist 
in designing tools, procedures, equipment, etc., but one 
thing readily apparent is that nobody is typical. Construct- 
ing an ore chute so that you can safely walk under it does 
not mean it is at a safe height for other people. Instructions 
written to make sense to an engineer may totally confuse 
someone else. 

Finally, human factors is not just common sense. Of 
course, human factors involves common sense, but it is more 
than that. Probably one reason why human factors seems 
like common sense is that human factors recommendations 
often make intuitive sense after they are explained. It is 
much like a mathematician's proof. Once it has been devel- 
oped, it is obvious; but arriving at the proof was a highly 
creative endeavor. Sometimes human factors information 
even runs counter to what some would call common sense. 
For example, it is common sense that increasing the inten- 
sity of an alarm will make the person respond faster. This 
appears true for simple responses, but it is not necessarily 
true for complex responses. In fact, increasing intensity may 
even cause the person to respond more slowly (29). Would 
common sense have predicted that surface irregularities 
could be detected more accurately when a person wears a 
thin cloth glove than when the bare fingers are used alone? 
It does not seem like common sense, but it is true (21). 



ROADBLOCKS TO THE APPLICATION OF HUMAN 
FACTORS 

Although it may be intuitively obvious that human fac- 
tors considerations in a system are central to maintaining 
production and efficiency, people have been somewhat slow 
in applying the principles to the design of workplaces and 
equipment. There are at least five common misconceptions 



that serve as roadblocks, and are often encountered when 
attempts are made to introduce human factors into an 
organization. 

1. All people are created equal. In fact, no two people 
are exactly alike. Systems must be designed to accom- 
modate the diversity in the population. When one size fits 
all, you can bet that the one size will fit all— poorly. 

2. People can be trained to overcome design deficiencies. 
This is true to some extent, but training can be somewhat 
unreliable. Under stress, people will respond the way they 
think systems should work, which may not be how the 
systems actually work. 

3. Engineers and designers know how people think and 
act. Engineers and designers may know how engineers and 
designers think and act, but engineers and designers do not 
necessarily think or act like everyone else. 

4. Minor human factors deficiencies are not important. 
Minor deficiencies often compound into major deficiencies. 
Minor deficiencies also have a way of insiduously eating 
into productivity and efficiency. Minor human factors defi- 
ciencies are much like minor hydraulic leaks; neither one 
can be ignored for long. 

5. No serious incidents indicate no human factors prob- 
lems. The Three Mile Island Nuclear Powerplant had 
numerous human factors deficiencies in the control room, 
and until the day the plant came within 60 min of 
meltdown, it had no serious incidents. 



HISTORY OF HUMAN FACTORS 

To appreciate the current state of human factors, it is 
instructive to know a little history about the discipline. 
Some would say that human factors started when the first 
cavedweller fashioned a rock to skin an animal, and formed 
the rock to fit the hand comfortably. For all practical pur- 
poses, the discipline of human factors started during World 
War II. 



1940-50— War Years 

It became apparent during World War II that the new, 
sophisticated equipment was exceeding operators' capabil- 
ities. At one time during the war, more pilots were lost in 
training than were lost in combat. Experimental psycholo- 
gists were asked to collaborate with engineers in designing 
various military hardware, including aircraft cockpits, 
radar consoles, combat information centers, and binoculars 
(10). 



1960-80— Recognition and Expansion 

As an indication of expansion during this period, the 
membership of The Human Factors Society grew to over 
3,000. Human factors expanded beyond the military-aero- 
space industry and entered civilian government and indus- 
trial organizations. It was during this period that the 
Bureau launched its human factors research efforts to im- 
prove safety in the mines. Human factors people were also 
employed by civilian industries to design and evaluate 
workplaces and consumer products. 



1980— A Household Word 

Advertisers have begun to use the terms "ergonomics" 
and "human-engineered" in advertisements for cars, lawn- 
mowers, truck seats, computer terminals, and even dental 
chairs. The following is a partial list of companies employ- 
ing human factors professionals (20): 



Aluminum Company 

of America 
AT&T 

Boeing Corp. 
Clark Equipment Co. 
Control Data Corp. 
Deere & Co. Corp. 
Eastman Kodak Corp. 
Federal Express Corp. 
FMC Corp. 
Ford Motor Co. 
General Electric 
General Motors Corp. 
Harris Corp. 
Hewlett Packard Corp. 
Honeywell, Inc. 



Hughes Aircraft 
IBM Corp. 
International Harvester 

Co. 
Liberty Mutual Insurance 

Co. 
Lockheed Corp. 
NCR Corp. 
Northrop Corp. 
Pitney Bowes 
RCA 

Rockwell International 
3MCo. 

Westinghouse Corp. 
Xerox Corp. 



Other professional organizations, including The Amer- 
ican Society of Mechanical Engineers, Institute of Electrical 
and Electronics Engineers, American Industrial Hygiene 
Association, and Society of Automotive Engineers have 
human factors or ergonomics subcommittees or technical 
groups. There are now about 60 graduate programs in 
human factors at universities in the United States (27). 

This brief history points out the early thrusts and cur- 
rent expansion of the human factors profession. The follow- 
ing section provides a brief historical look at human factors 
in mining, with an emphasis on the research activities of 
the Bureau. 



1950-60— Birth of a Profession 



HISTORY OF HUMAN FACTORS IN MINING 



After the war, human engineering or engineering psy- 
chology laboratories (as they were called then) were estab- 
lished by the Navy and Air Force. Activity was maintained 
almost exclusively within the military-industrial complex. 
During this period, the Soviet Union launched Sputnik, and 
the race for space began. The industry that built planes and 
guns now turned to space, and with that came human fac- 
tors. The Ergonomic Research Society of Great Britain was 
formed in 1950, and The Human Factors Society in the 
United States was established in 1957. In 1960, the mem- 
bership of The Human Factors Society was 500. 



Human factors concerns are often stimulated by the in- 
troduction of new technology into the workplace. In the min- 
ing industry, new technologies have had their greatest im- 
pact in the underground environment. On the other hand, 
surface mining innovations have typically been in terms 
of increased size and efficiency of earth- and ore-moving 
equipment, and for the most part, have not involved the 
introduction of revolutionary new technologies. 

Underground mining, before mechanization, was back- 
breaking, dangerous work: picks and shovels were state- 
of-the-art. Miners could spend 3 to 6 h undercutting a coal 



face. As shown in figure 1-2, this was done lying on their 
sides and using picks to make a horizontal slit 3 to 4 ft deep 
at the bottom of the seam. 

1870-1950— Early Mechnization 

Mechanization of underground mining really began in 
the 1870's. At the beginning of the decade, steam locomo- 
tives were introduced underground. Early attempts were 
made to mechanize loading, but they did not attract much 



attention. In the latter part of the decade, cutting machines 
were introduced to undercut the coal face. Figure 1-3 depicts 
two miners operating an early Harrison Pick cutting ma- 
chine. A little over a decade after cutting machines were 
introduced, the first electrically driven drill was used. These 
early machines were extremely noisy, vibrated so violently 
that they caused internal injuries, and liberated more dust 
and methane than could be handled by the ventilation 
systems. Technology moved slowly in the mining industry 
and by 1915, almost 40 yr after the introduction of cutting 




Figure 1-2.— Undercutting a COal face before mechanization. (Courtesy of National Archives, Washington, DC) 




Figure 1-3.— Early Harrison Pick Cutting macnine. (Courtesy of National Archives, Washington, DC) 



machines, only about one half of the Nation's coal output 
was mined by such machines (6). It was not until 1930 that 
the industry fully mechanized the undercutting operation. 
Mechanical loading of coal increased during the 1920's and 
1930's (28), but it was not until 1943-44 that more coal was 
mechanically loaded than was loaded by hand (24). 
Although electric locomotives were generally accepted in 
the early 1900's, West Virginia still reported 1,600 animals 
used for haulage in 1938. A common sight was the horse- 
drawn mine car shown in figure 1-4. 

During this early mechanization period, the Bureau was 
established (1910) as part of the Department of the Interior. 
It was initially set up as strictly an information-gathering 
agency. Not until 1941 was the Bureau given authority to 
enter and inspect underground coal mines. 

1950-70— Modern Mechanization and the Coal Act 

The next "revolution" in underground mining was the 
introduction of continuous mining machines. Actually, ex- 
perimental models were being tested in several mines dur- 
ing the late 1940's. Initially, the industry was skeptical, 
but as larger and more powerful machines were developed, 
the skepticism slowly abated. The machines were widely 
adopted in the late 1950's and early 1960's. Early continu- 
ous mining machines were not much different in appearance 
from machines in use today. 

During this period, there was virtually no human fac- 
tors research being conducted in the United States, despite 



the growing recognition of human factors in the military 
and aerospace industries. In Europe, however, some human 
factors work was being done, but on a limited and frag- 
mented scale. In 1969 the National Coal Board in England 
established the Institute of Occupational Medicine, which 
was chartered to conduct ergonomic research for under- 
ground coal mining. 

In 1968, a mining disaster in Farmington, WV, killed 
78 workers. One year later, the U.S. Congress passed the 
Federal Coal Mine Health and Safety Act of 1969. This act 
gave enforcement powers to the Bureau and significantly 
broadened its mandate regarding health and safety research 
in coal mining. 



1970— Birth and Growth of Human Factors in Mining 

After the passage of the 1969 coal act, the Bureau began 
sponsoring human factors research programs. The first for- 
mal human factors project was a problem identification 
study in underground coal completed in 1971 (19). That 
study proposed research dealing with equipment design, 
personal protective equipment, communications, illumina- 
tion, noise, roof testing, and training. That was followed 
a year later by a review of the human performance litera- 
ture (11) in which only 49 documents (mostly European) 
could be found that addressed mining-related tasks and 
contained quantitative results or factual support for 
conclusions. 




Figure 1-4. — Use Of animaiS for hauling COal. (Courtesy of National Archives. Washington. DC) 



In the next few years, the Bureau sponsored projects to 
address identified problems (19). One project investigated 
the standardization of controls for underground electric face 
equipment and focused on the development of design guide- 
lines that would provide some degree of consistency in 
control configurations for this equipment (15). Another proj- 
ect involved machine canopies, in particular the fabrication 
and evaluation of overhead protective structures for under- 
ground equipment operators (1-2, 8-9, 17-18). A project 
that dealt with optimized operator compartments integrated 
and extended the results of earlier work by developing and 
validating design guidelines for underground mining-equip- 
ment operator compartments (3, 12, 22). The Inherently Safe 
Mining Systems project developed and demonstrated equip- 
ment modifications for improved safety in conventional and 
continuous coal mining systems (13). 

During the early and mid-1970's, a series of disasters 
rocked the industry. In 1977 Congress passed another mine 
safety and health act that extended the 1969 act to metal 
and nonmetal mining, shifted enforcement to the Depart- 
ment of Labor (Mine Safety and Health Administration), 
and made provisions for mandatory training regulations. 
Much of the early human factors work in underground coal 
was applicable to underground metal and nonmetal mines 
because the same equipment was used. Nevertheless, 
differences did exist, and in the 1980's two human factors 
problem identification studies were launched for the under- 
ground metal-nonmetal industry (16, 25). 

The majority of human factors research has been con- 
ducted for the underground environment, but surface 
mining has also attracted some of the attention of human 
factors researchers. One area that received early attention 
in surface mining was the problem of limited visibility (field 
of view) from large haulage trucks (14, 23). In 1982, two 
human factors problem-identification studies directed at 
surface mining were published. One dealt with the mining 
process itself (4), and the other with processing plants (5). 

It is apparent from this brief historical review that 
human factors research in the mining industry has been 
a relatively recent development, spurred on by advances 
in technology and the recognized need to improve safety and 
productivity. As will be seen in subsequent chapters, there 
is a large body of human factors data, principles, and 
methods, developed outside the mining industry, that can 
be brought to bear on problems encountered within the in- 
dustry today. 



COVERAGE 

The remaining chapters will review in more depth 
human factors concepts applicable to the mining industry 
and review much of the quickly expanding human factors 
in mining literature. Chapters 2, 3, and 4 present basic foun- 
dational information: the role of human factors in system 
design, including analytical tools used by human factors 
specialists; a review of human capabilities and limitations 
that form the basis for many design decisions; and the role 
of human error in accidents. 

Chapters 5, 6, and 7 deal with design of equipment and 
tasks. Special emphasis is given to the design of work that 
involves physical labor because, despite the advances in 
mechanization, there still remain numerous tasks involv- 
ing lifting, carrying, etc. Chapter 8 focuses on the environ- 
ment and its impact on human performance. The four 



environmental stressors discussed are illumination, ther- 
mal conditions, noise, and vibration. The last two chapters 
deal with topics traditionally subsumed under industrial 
and organizational psychology, including training, motiva- 
tion, and organizational development. 

REFERENCES 

1. Billmayer, H. Study of Low Coal Canopy Concepts (contract 
H0346102, Bendix Corp.). BuMines OFR 70-76, 1975, 39 pp.; NTIS 
PB 254 301. 

2. . Development of Protective Canopy Concepts for 

Underground Rail Haulage (contract H0357091, Bendix Corp.). 
BuMines OFR 76-76, 1976, 85 pp.; NTIS PB 254 504. 

3. . Fabrication and Evaluation of Optimized Operator Com- 
partments (contract H0252048, Bendix Corp.). BuMines OFR 79-78, 
1976, 34 pp.; NTIS PB 284 023. 

4. Conway, E.J., and M.S. Sanders. Recommendations for Human 
Factors Research and Development Projects in Surface Mining (con- 
tract J0395080, Canyon Res. Group Inc.). BuMines OFR 211-83, 
1982, 86 pp.; NTIS PB 84-143650. 

5. Cross, B., and J. Schurick. Hazard Analysis and Safety 
Economics in Mineral Processing Plants. Canyon Res. Group Inc., 
Westlake Village, CA, 1982, 163 pp. 

6. Dix, K. Work Relations in the Coal Industry: The Hand Load- 
ing Era, 1880-1930. Inst, for Labor Studies, WV Univ., Morgan- 
town, WV, 1977, 77 pp. 

7. Eastman Kodak Co. Ergonomic Design for People at Work. 
Volume I: Workplace, Equipment, and Environmental Design and 
Information Transfer. Lifetime Learning, 1983, 406 pp. 

8. Farrar, R. Design and Development of Protective Canopies for 
Underground Low Coal Electric Face Equipment, Including Shut- 
tle Cars. Final Report (contract H0220031, Bendix Corp.). BuMines 
OFR 3(l)-75, 1973, 241 pp.; NTIS PB 240 541. 

9. Farrar, R., R. Champney, and L. Weiner. Survey on Protec- 
tive Canopy Design (contract H0242020, Bendix Corp.). BuMines 
OFR 50-76, 1974, 163 pp.; NTIS PB 251 672. 

10. Fitts, P. Engineering Psychology and Equipment Design. 
Ch. in Handbook of Experimental Psychology, ed. by S. Stevens. 
Wiley, 1951, pp. 631-674. 

11. Fried, C. The Miner, His Job and His Environment: A Review 
and Bibliography of Selected Recent Research on Human Perfor- 
mance (contract H0122019, Natl. Bureau of Standards). BuMines 
OFR 27-72, 1972, 192 pp.; NTIS PB 211 732. 

12. Gunderman, R. Optimized Operator Compartments (contract 
H0252092, Dresser Industries). BuMines OFR 71-79, 1979, 94 pp.; 
NTIS PB 297 668. 

13. Hamilton, D.D., J.E. Hopper, and J.H. Jones. Inherently Safe 
Mining Systems. Executive Summary (contract H0111670, FMC 
Corp.). BuMines OFR 124-77, 1977, 38 pp.; NTIS PB 271 150. 

14. Hawley, K.W., and S.F. Hulbert. Improved Visibility Systems 
for Large Haulage Vehicles (contract H0262022, MBAssoc). 
BuMines OFR 100-78, 1978, 121 pp.; NTIS PB 286 065. 

15. Hedling, W.G., and R.J. Kennihan. Standardization of Con- 
trols for Underground Electric Face Equipment. Final Report (con- 
tract H0230021, Applied Science Assoc. Inc.). BuMines OFR 
45(l)-75, 1974, 279 pp.; NTIS PB 242 562. 

16. Helander, M., and G. Krohn. Human Factors Analysis of 
Underground Metal and Nonmetal Mines (contract H0308067, 
Canyon Research Group Inc.). BuMines OFR 16-84, 1983, 99 pp.; 
NTIS PB 84-158732. 

17. Hermanson, W. Fabricate and Evaluate Protective Canopies 
for 3-Foot Coal Seams (contract H0357090, Bendix Corp.). BuMines 
OFR 42-77, 1976, 157 pp.; NTIS PB 265 073. 

18. Hermanson, W., and H. Billmayer. Design and Development 
of Protective Canopies for Shuttle Car, Loader, and Roof Drill (con- 
tract H0242028, Bendix Corp.). BuMines OFR 4-76, 1974, 39 pp.; 
NTIS PB 248 833. 

19. Hitchcock, L., and M. Sanders (eds.). Survey of Human Fac- 
tors in Underground Bituminous Coal Mining. Naval Ammunition 
Depot, Crane, IN, 1971, 137 pp. 



20. Knowles, M. (ed.). The Human Factors Society 1983 Direc- 
tory and Yearbook. The Human Factors Society, 1983, 279 pp. 

21. Lederman, S. Heightening Tactile Impressions of Surface Tex- 
ture. Ch. in Active Touch, ed. by G. Gordon. Permagon, 1978, pp. 
205-214. 

22. McGuirk, F.D., and G.A. Podgornik. Optimized Operator Com- 
partment. Final Report (contract H0242033, Applied Science Assoc. 
Inc.). BuMines OFR 126(l)-76, 1975, 50 pp.; NTIS PB 261 490. 

23. Miller, W. Analysis of Haulage Truck Visibility Hazards at 
Metal and Nonmetal Surface Mines, 1975. MSHA IR 1038, 1976, 
19 pp. 

24. National Academy of Sciences. Toward Safer Underground 
Coal Mines. 1982, 190 pp. 

25. Perry, T., N. Schwalm, and W. Crooks. Human Factors Anal- 
ysis of Underground Work Areas and Tasks in Metal and Nonmetal 



Mines (contract J0387230, Perceptronics Inc.). BuMines OFR 
111(1)-81, 1981, 150 pp.; NTIS PB 81-236804. 

26. Rogers, J., and R. Armstrong. Use of Human Engineering 
Standards in Design. Human Factors J., v. 19, No. 1, 1977. pp. 
15-23. 

27. Sanders. M., and L. Strother. (eds.). Directory of Graduate 
Human Factors Programs in the U.S.A. The Human Factors Soci- 
ety, 1985, 57 pp. 

28. Smith, C, and C. Ball (eds.). Mechannual 1939. Mechaniza- 
tion Inc., 1939, 437 pp. 

29. Van der Molen, M.. and P. Keuss. The Relationship Between 
Reaction Time and Intensity in Discrete Auditory Tasks. Q.J. 
Exper. Psych., v. 31, 1979. pp. 95-102. 



CHAPTER 2.— HUMAN FACTORS IN THE DESIGN OF SYSTEMS 




Effective system design should include system definition, task analysis, efficient interface design, and field 
testing. 



As indicated in chapter 1, a central concept in human 
factors is the system. Although various authors use different 
definitions for the term, a very simple one is used here. A 
system is an entity that exists to carry out some purpose 
(2). 1 A system is composed of humans, machines, and other 
things that work together (i.e., interact) to accomplish some 
goal that these same components could not produce inde- 
pendently. Using systems concepts serves to structure the 
approach to the development, analysis, and evaluation of 
complex collections of humans and machines. According to 
Bailey (2) 

The concept of a system implies that we recognize a 
purpose; we carefully analyze the purpose; we under- 
stand what is required to achieve the purpose; we 
design the system's parts to accomplish the require- 
ments; and we fashion a well-coordinated system that 
effectively meets our purpose. 

This chapter first discusses the major characteristics of 
a system, using a haulage vehicle in an underground mine 
as the focus. The chapter then traces the development of 
a system and indicates the various human factors activities 
that could be applied to insure the resulting system meets 
its stated objectives. 



CHARACTERISTICS OF SYSTEMS 

In discussing the various characteristics of systems it 
will be helpful to have an example that illustrates the 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



various concepts. In underground mining, both coal and 
noncoal, haulage vehicles are used to move the coal, or ore, 
from the working face to a more permanent continuous 
haulage system, usually a conveyor belt system or train. 
Examples of such haulage vehicles are front-end loaders, 
scoops, shuttle cars, and load-haul-dump (LHD) vehicles. 
These vehicles are run by batteries, diesel motors, or elec- 
tricity supplied by cable. They are operated by a single 
operator, although the operator may have a helper to assist. 
In some cases the vehicle picks up the coal or ore itself, as 
in the case of a scoop or LHD; in other cases the vehicle 
is loaded by another machine, as in the case of shuttle cars. 
Given this basic concept of an underground haulage vehi- 
cle, the following is a discussion of the characteristics of 
systems. 

Systems Have a Purpose 

In Bailey's definition of a system (2), it was stressed that 
a system has a purpose. Every system must have a purpose, 
or it is nothing more than a collection of odds and ends that 
coexist. The purpose of a system is the system goal or ob- 
jective, but systems can have more than one purpose. The 
goals of a system should be stated in general terms so that 
they need not be changed every time something in the 
system changes. Appropriate system goals for a haulage 
vehicle would include 

Haul ore (or coal) from the working face to the continuous 
haulage system. 
Load ore (or coal) from the floor. 
Protect the operator from roof falls. 



10 



It is important that the goals or objectives of the system 
be clearly understood and agreed upon before designing, 
developing, or evaluating a system. For example, the com- 
mon typewriter keyboard (QWERTY, so named for the first 
six keys of the first letter row) has been criticized as ineffi- 
cient and slow. The most common letters are positioned for 
the left hand, and common letter combinations require 
awkward finger movements. Actually, when the goal of the 
system is understood, the keyboard organization has a pur- 
pose. When typewriters were first invented, fast typists 
could easily jam the keys. The keyboard, therefore, was 
actually designed to slow the typist down and to separate 
common letter combinations (e.g., QU) so that the key bars 
would not come from the same side of the machine and jam. 
As this example illustrates, failure to understand the goals 
of a system can lead to irrelevant evaluations. It must be 
pointed out, however, that one can challenge the adequacy 
and relevance of system goals. With the advent of element 
balls, daisy wheels, and word processor printers, there is 
no need to slow down typists because there are no keys to 
jam. 

Systems Are Hierarchical 

A system can be considered to be a part of a larger 
system and, when analyzed, the system itself can be com- 
posed of more molecular systems (also called subsystems). 
This is illustrated in figure 2-1, where a haulage vehicle 
system is shown as one subsystem in the larger mine 
haulage system, which in turn is one subsystem in the even 
larger mine system. A closer look at the haulage vehicle 



Total mine 



Exploration 



Extraction 



y/Am&'/zi 



Trains 



Processing 



Conveyors 



=F 



/ehicle'^^ 



Propulsion [ 



Steering 



Braking 



UM^WA 



Sensing | 



Information 
processing 



Action I 



Memory 



Figure 2-1 .—Schematic diagram of haulage vehicle subsystem 
within the total mine system. 



subsystem shows that it is composed of a vehicle subsystem 
and an operator subsystem. Each of these in turn is com- 
posed of more molecular systems, such as the propulsion 
system or the steering system. When faced with the task 
of describing or analyzing a system, one often asks: "Where 
do you start?" and "Where do you stop?" The answer to both 
these questions is: "It depends." 

In describing and analyzing a system two decisions must 
be made. First, one has to decide on the boundary of the 
system; that is, what is to be considered part of the system 
under study, and what is to be considered outside the 
system? There is no right or wrong answer, but the choice 
must be logical and result in a system that performs an iden- 
tifiable function. Thus, one could focus on the haulage 
vehicle as the system and consider conveyors and trains as 
outside the system. Alternatively, one could focus on the 
mine haulage system, with haulage vehicles as one sub- 
system or component of the larger system. 

In some systems it appears that the designers drew the 
boundary of the system in such a way that the operator and 
maintainer of the equipment were considered outside the 
system. When this sort of design philosophy prevails, one 
finds systems that are difficult to operate, require excessive 
training, are prone to operator errors, and are difficult to 
maintain. As a general rule, one should always include 
operators and maintainers inside the system boundary to 
help insure that the system is designed to accommodate and 
facilitate human performance and safety. 

The second decision that must be made is to set the limit 
of resolution for the system. That is, how far down into the 
system do you want to go? At the lowest level of analysis 
are components. A component in one analysis may be a sub- 
system in another analysis that uses a more detailed limit 
of resolution. Focusing on the haulage vehicle as a system, 
the analysis can be limited and the vehicle and operator 
can be considered the components. Alternatively, the anal- 
ysis could be extended to consider the vehicle and operator 
as subsystems and things such as propulsion and steering 
as the components. As with setting system boundaries, there 
is no right or wrong limit of resolution. The proper limit 
depends on why one is describing or analyzing the situa- 
tion in the first place. 

Systems Operate in an Environment 

The environment of a system, whether a closed- or open- 
loop system, is everything outside its boundary; therefore, 
the environment of a haulage vehicle system includes the 
roadways of the mine; other vehicles, objects, and people 
in the area; the conveyor system; the loading machine: etc. 
An open-loop system cannot sense its own actions and can- 
not alter its course of action. On the other hand, a closed- 
loop system can sense its own action and alter its course 
based on that information. 

Humans are inherently closed-loop systems. To illus- 
trate the difference, a haulage vehicle, without a driver, 
would be considered an open-loop system when the vehicle 
rolls down a slope. There is no mechanism to feed back in- 
formation to the system regarding its position relative to 
obstacles in the environment or to take corrective action 
to avoid them. The same haulage vehicle, with a driver 
maneuvering down a roadway, is a closed-loop system. The 
operator functions in the feedback loop, sensing the posi- 
tion of the vehicle and the position of obstacles in the en- 
vironment, and changing the course of the vehicle to avoid 
the obstacles. 



11 



Components Serve Functions 

Every component (the lowest level of analysis) must 
serve at least one function in the system. Further, these 
functions must be related to the fulfillment of one or more 
of the system's goals or objectives. One of the tasks of human 
factors specialists is to aid in making decisions as to whether 
humans or machines (including computer software) should 
carry out a particular system function. For example, who 
or what should limit the speed of a haulage vehicle system? 
Should a speed governor be installed to automatically limit 
speed, or should that function be given to the driver? Who 
should be responsible for sensing the speed of the vehicle? 
Can a human estimate speed accurately enough, or should 
a speedometer be provided as a component in the system? 
By understanding the capabilities and limitations of 
humans, human factors specialists can provide valuable in- 
formation to the decisions regarding allocation of function. 

Humans serve various functions in systems (7). These 
functions involve 

1. Sensing (seeing, hearing, feeling), 

2. Storage (memory), 

3. Information processing (thinking), 

4. Decisionmaking, and 

5. Action (movement, speaking). 

Components Interact 

To say that components interact simply means the com- 
ponents work together to achieve system goals. Each com- 
ponent has an effect, however small, on other components. 
One of the outcomes of a systems analysis is the descrip- 
tion and understanding of these component and subsystem 
interactions. 

Systems, Subsystems, and Components Have 
Inputs and Outputs 

At all levels of a system there are inputs and outputs. 
The outputs of one subsystem or component are the inputs 
to another. It is through inputs and outputs that components 
and subsystems interact. Inputs can be physical entities 
(such as materials and products), electrical impulses, 
mechanical forces, or information. As illustrated in figure 
2-2, a haulage vehicle outputs information on speed from 
its speedometer. That information becomes an input to the 
operator subsystem. The operator subsystem processes the 
information and outputs an action; e.g., stepping on the 
brake. That mechanical force then becomes an input to the 
braking subsystem of the vehicle. 




Output 



c=E> 



Input Speedometer 



Output 



Input M 

W* j ! Output 

ll 
II 

Input 



Accelerator 



Figure 2-2.— Schematic diagram of inputs and outputs between 
subsystems of a system. 



An analysis of a system must specify all the inputs and 
outputs required for each component and subsystem to per- 
form its functions. Human factors specialists are especially 
qualified to determine the inputs and outputs that are 
necessary for the human component to successfully carry 
out its functions. Failure to supply adequate and proper in- 
puts or the facilities necessary to produce outputs will result 
in degraded system performance. For example, how appro- 
priate is an auditory warning of excessive speed in an 
underground mine? Which is more appropriate for input- 
ting steering commands to the vehicle, a wheel or a joystick? 

From this short overview, it can be seen that systems 
have a purpose and are made up of subsystems and com- 
ponents interacting through inputs and outputs to perform 
functions in support of system objectives. Systems operate 
within an environment, but the definition of what is part 
of the system and what is part of the environment is a some- 
what arbitrary decision made to facilitate analysis and 
evaluation. With this in mind, a discussion of the system 
design process and the types of activities that human fac- 
tors specialists conduct is presented. 



HOW ENGINEERS REALLY DESIGN 

Several earlier studies that addressed the question of 
how engineers design and how they make use of human fac- 
tors information in the design process were analyzed (8). 
Forty-four mechanical and electrical engineers, each with 
approximately 15 yr of experience, served as subjects in the 
studies. Basically, a design problem was presented to the 
engineers, and information was provided them during the 
design process. The tasks, or design problems, included de- 
signing a command-control console, a circuitboard tester, 
an air traffic control radar-monitoring console, and test 
equipment to check an electronic subsystem. Each problem 
took several days to complete. 

What this analysis (8) found was that "almost im- 
mediately after examining the problem, they (the engineers) 
started to design hardware without performing much delib- 
erate, systematic analysis." Little or no consideration was 
given to how the equipment was to be used by the operator, 
the sequence of use, or which functions were most impor- 
tant or most frequently used. No attempts were made to 
allocate functions between people and hardware. In essence, 
the engineers appeared to skip over the first two stages of 
system development. The engineers relied overwhelmingly 
on design solutions that they had used before. This 
prevented them from considering novel approaches to the 
designs. Further, there was a reluctance to modify their in- 
itial designs, except in minor respects when new informa- 
tion was made available to them. For example, halfway 
through the process the engineers were told that instead 
of four people to operate the console, only two could be used. 
This resulted in only minor changes in the placement of 
displays and controls, but no overall revision of the basic 
design concept. 

As far as the attitudes of the engineers toward human 
factors was concerned, the analysis (8) concluded that: "One 
of the most consistent findings of our research, confirmed 
in each study with all subjects regardless of sophistication, 
years of experience, or type of design problem, is that the 
typical design engineer does not consider human factors in 
his design." In questioning the engineers during the anal- 
ysis, however, it was found that they had a strong, profound 
interest in human factors and a dedication to consider 



12 



human factors in their designs. These verbal statements, 
however, were totally inconsistent with their actual be- 
havior on the design problems. 

Although this analysis was carried out over 15 yr ago, 
the situation, while improved, is still not much different 
today. Recently, one of the authors of this Information Cir- 
cular was called upon to evaluate the human factors aspects 
of a large demineralizer panel. The engineers who laid out 
the displays on the console did not know what information 
the operator needed to run the panel, the operating se- 
quence, how often various displays would be used, or the 
importance of various displays in operating the system. 
Despite this, they had no misgivings about placing the 
displays on the panel. 

STAGES IN THE DESIGN OF SYSTEMS 

Systems do not just spring into life; they go through a 
process of development. Sometimes the process is structured 
and the stages are easy to identify. More often, systems are 
developed in a more fluid, unstructured manner, where it 
is almost impossible to separate the various stages of their 
development. When a manufacturer develops a new bucket- 
wheel excavator for a surface mine, it is likely that the 
stages of development are carefully planned and executed. 
When the superintendent of a surface mine puts together 
an all-purpose maintenance vehicle, the stages of develop- 
ment are passed through more informally. Although the 
same sorts of decisions and considerations may be involved, 
the process is not as systematic or exhaustive as it is por- 
trayed in this chapter. 

Six stages in the design of a system are listed by Bailey 
(2). These stages are depicted in figure 2-3. Dividing the 
design process into stages gives the impression of a simple 
linear process. In actual practice, however, the process is 
iterative; that is, it cycles over and over, becoming more 
detailed in each pass through the stages. Information devel- 
oped in a later stage may influence decisions made in earlier 
stages, thus requiring a reappraisal. The concept of a sur- 
face mining all-purpose maintenance vehicle will be used 
to illustrate the various stages in the design of a system. 

Stage 1 : Determine Objectives and System 
Specifications 

As already discussed, one cannot design a system 
without a clearly stated set of objectives. The objective of 
the maintenance vehicle is to carry the required tools, equip- 
ment, parts, and personnel to perform maintenance tasks 
on equipment in the field. Performance specifications state 
what the system must do to meet its objectives. These re- 



STAGE I 
Determine objectives 

and 
system specifications 



STAGE 2 
Definition of system 



STAGE 3 
Basic design 



STAGE 4 

Interface 
design 



STAGE 5 

Facilitator 

design 



STAGE 6 
Testing 



Figure 2-3.— Stages in the development of a system (based 
on stages suggested by Bailey (2) ). 



quirements are derived from a careful study of user needs. 
Typically, according to Bailey (2), the information is col- 
lected using interviews, questionnaires, site visits, and work 
studies. Usually, constraints are part of the system require- 
ments. For example, a maintenance vehicle has to operate 
in mud, in high winds, and in temperatures below freez- 
ing. System designers must also deal with constraints 
related to the human component of the system. These relate 
to the skills, knowledges, and capabilities of the operators, 
and the number of people required to operate the system. 
For example, one constraint for the maintenance vehicle 
might be that it can carry at least two people. 

Stage 2: Define the System 

The second stage involves listing the functions that the 
system must perform to achieve the objectives and system 
specifications defined in stage 1. Some functions of the 
maintenance vehicle system would include 

Transporting people and equipment to the worksite. 

Fixing hydraulic leaks, 

Welding broken parts, 

Lifting objects weighing up to 1 st, and 

Communicating with the base maintenance shop. 
During this stage, people-related information would also 
be collected. This would include information regarding the 
availability of people and the basic characteristics of the 
potential user population (operators and maintainers), such 
as size, education, skills, and abilities. In some cases the 
constraints of the system will be modified as information 
concerning the available labor pool is obtained. For exam- 
ple, it may not be feasible to use a highly technical system 
if the operators lack the required skills to understand it. 

Stage 3: Basic Design 

In this stage the functions identified in stage 2 are 
allocated to human or machine, and the resulting tasks of 
the human are analyzed. Central to this activity is the proc- 
ess of task analysis. Task analysis is the process by which 
the human's functions are broken down into required ac- 
tivities, and each activity is analyzed to determine human 
and system requirements needed to successfully carry out 
the particular activity. 

Task analysis is probably the most important and fun- 
damental process performed by human factors specialists. 
Its use transcends system design and becomes the basic tool 
for understanding the human component in any system. 
Task analysis is as much an art as it is a science. It involves 
a series of methodologies for collecting task data and various 
formats for presenting the information. It will not be pos- 
sible to cover all the facts of task analysis in this report. 
The reader interested in more information can refer to 
reference 9. 

Table 2-1 lists the various methods that can be used to 
collect task analysis information. Generally, more than one 
method is used to insure that complete and accurate in- 
formation is obtained. One of the most comprehensive 
examples of task analysis for the mining industry was car- 
ried out by Crooks (3) in which virtually all underground 
metal-nonmetal unit operations were analyzed. Examples 
of unit operations included feedleg drilling, rock bolting, 
sand filling, slusher operation, track maintenance, timber 
construction, and ore skip operation. The task analysis 
team, with an •expert' - (supervisor, safety engineer, etc) 



13 



present, conducted onsite observations of workers perform- 
ing the various unit operations. The team followed up the 
observations by conducting two-person, group interviews 
with experienced workers away from their jobs. A minimum 
of four workers were interviewed for each unit operation. 
After completion of the interviews, technical conferences 
with one or two supervisors were held to verify the com- 
pleteness of the information collected. A total of 188 inter- 
views were conducted to analyze 43 unit operations. Each 
of the unit operations (e.g., feedleg drilling) was broken 
down into tasks (e.g., prepares drill, drills, maintains drill), 
and each task was further analyzed into activities (e.g., col- 
lars hole, drills hole, removes bound steel). 

Table 2-1.— Methods of collecting task analysis information 

Observation Observe worker performing job. 

Interview: 

Observational Observe and interview worker while per- 
forming job. 

Individual Interview worker away from jobsite. 

Group Interview more than one worker at same 

time, away from jobsite. 

Technical conference Interview subject matter experts or super- 
visors regarding job of worker. 

Checklist Worker checks tasks that are performed on 

the job from a master list. 

Questionnaire Open-ended questions that worker answers 

regarding work tasks. 

Diary Worker keeps a record of job activities 

throughout day. 

Motion picture Motion pictures are made of worker per- 
forming specific tasks. 

The type of information collected in a task analysis 
depends on the purpose of the analysis. For example, task 
analysis information can be used for determining training 
requirements for a task, for assessing hazards and unsafe 
conditions or procedures involved in a task, for designing 
or modifying equipment or procedures, or for determining 
the type and level of people needed to operate and main- 
tain a system. As another example, a task analysis approach 
to determine visibility requirements for operation of con- 
tinuous miners, shuttle cars, and scoops in underground coal 
mines was used by Sanders and Kelley (10). It is also worth- 
while by way of illustration to point out that the following 



task analysis data were collected by Crooks (3) for under- 
ground metal-nonmetal tasks: 

Minimum and maximum times to complete. 

Amount of training required. 

Percentage of time standing. 

Physical energy level required. 

Degree to which 12 classes of physical activities (such as 
climbing, stooping, handling, talking) were present. 

Degree to which six classes of visual requirements (such 
as near acuity, depth perception, color vision) were present. 

Generic classes of hazards involved (such as electrical, hot- 
cold surfaces, sharp objects, explosives). 

Common errors or accidents. 

Principal visual features involved in performing the task. 

Type of illumination usually present. 

Worksites where the unit operation was performed. 
This is a rather extensive list of information for a single 
task analysis. Several of the items in this tabulation were 
included because a primary purpose of the analysis was to 
establish illumination requirements for the unit operations. 
The various formats used for presenting task analysis 
information depend, of course, on what information is col- 
lected and on the purpose of the analysis. Common formats 
include column format, operational sequence diagrams, and 
timelines. ' 

With a column format, the steps or activities compos- 
ing a task are listed down the page, and the information 
categories are listed across the top of the page. For each 
step or activity, the required information is filled in across 
the page. Figure 2-4 is an example of a column format. 

Operational sequence diagrams depict the sequence of 
steps and the interrelationships among the components of 
a system in carrying out a particular task. Standard sym- 
bols are used to present the information. Figure 2-5 pre- 
sents an example of an operational sequence diagram for 
handling an emergency in a steam generation plant (6). 
Timelines depict the activities performed along a time 
scale. Where several persons, or persons and machines are 
interacting, a timeline presentation can graphically illus- 
trate periods of overload and underload during the execu- 
tion of a task. Figure 2-6 shows an example of a timeline 
generated by a computer program developed by the Na- 
tional Coal Board in England (11). 



Direction 



3. Position miner 
in entry 



Operator Task 



Maneuver machine to line up 

overhead paint markings with 
a known point on either side 
of the cutting head that will 
yield the planned entry width 
while keeping machine clear 
of ribs and roof. 



Tram to face while raising 

or lowering cutting head to 
starting elevation and while 
lowering the gathering head. 



Helper Task 



Lift and pull cable into 
place along the right 
rib so that it is out of 
the way of the crawler 
tracks as the miner is 
trammed forward and 
back. 




Comments 



Foreman painted centerhne 
on ceiling Bolt crew hung 
a reflector on the last row 
of bolts to show boundary 
of safe roof. 



Different operators take 
different approaches to 
starting point for cutting 
operation (top, middle, or 
bottom). Some would bump 
into the middle of the face 
and then tram back a few 
inches and start head 
rotation. 



Controls 



Tram levers. 

Conveyor boom elevation lever. 

Conveyor boom swing lever. 



Tram levers. 

Cutting head elevation lever. 

Gathering head elevation lever. 



Displays or feedback 



View of roof and painted 

centerline 
View of reflector on last 

row of bolts. 



View of cutting head 
position. 

View of gathering head 

position. 
View of face relative to 

machine. 
Sound of cutting head 

bumping into face. 
View of ceiling paint marks 

relative to cutting head 
View of machine relative 

to ribs. 
View of helper and cable. 



Figure 2-4.— Example of a column format used in task analysis. 



14 




il 
I 

m 
i 

l 
i 

^Telephones auxiliary 
operator 

Directs to verify that flash 
evaporator valve is closed 
to make related adjust- 
ments, and to shut 
city water supply to 
flash evaporator tank 



Figure 2-5.— Example of an operational sequence diagram (OSD) used in task analysis (6). (Copyright 1984. Electric Power Research institute. 

Report NP-3659, "Human Factors Guide For Nuclear Power Plant Control Room Development." Reprinted with permission.) 



Surface simulation study on cam packing 
2- shift production, 3-shift ripping 



15 



h min 
- 



External delays 



~ 10 ~. 
- 20 A 
~ 30 A 
"40 A 

~ 50 A 

1 - A 
I " 10 
I " 20 -j 
I - 30 A 
I " 40 A 
I - 50 



2 - 



Main gate rip 
cam packing 



Rip preparation, 
protect cables 



-L 



Prepare scaffold 
to drill 



Complete advance 
m/g end I AFC 
2 ft 

Cut on snake 
tail to main- 
Obtain drill rod, 
drill II 4-ft holes 



Stem and charge 
6 holes 



I 



Advance roadhead 
space and cam 
loader 
Fire 4 ft, 6 holes 



Trim loose stone 



Fill to cam feeder 
Stem and charge 



f 



No. I machine 
at main gate 



Machine preparation 



Cut on snake main 
to tail 20 yd 



0/C dozer doors 



Advance r/h supports, 

extend r cantilever 

2 ft, advance 



^— Cut on snake 
Wait.AFC standing 



0/C dozer doors 



Flit to buttock 20yd 



Cut main to tail 



Advance main 
gate end 



Cut main to tail 
160 yd 



Wait, AFC standing 
fire main gate rip 



Cut main to tail 
160 yd 



^ 



Cut into No. 2 



No. 2 machine 
at tailgate 



Machine preparation 



Cut on snake tail 
to main 20 yd 



Flit cleanup main 
■to tail 20yd- 



Wait.AFC standing 



Flit tail to main 20 yd 



^-Advance AFC 
Advance tail gate end 



Advance 16 powered 
supports 



Cut main to tail 20yd 
Flit cleanup 



-¥ 



Wait AFC standing 



Flit cleanup 
Flit main to tail 20 yd 



Change picks 



Wait.No. I machine 
to remove buttock 



Figure 2-6.— Example of a timeline used in task analysis (11). (Courtesy of Butterworth scientific Ltd.) 



16 



The information obtained from the task analysis phase 
of system design represents the primary source of data for 
the remaining stages of the design process. Again, it should 
be pointed out that the design process and task analysis 
are iterative in nature. As more and more details are de- 
fined in the system, more and more details can be added 
to the task analysis. This serves to verify system design deci- 
sions and to point the way toward further refinements in 
the system. 

Stage 4: Interface Design 

Based on the information collected and decisions made 
in stage 3, the designer moves to a more molecular level 
and begins designing the human-equipment and human- 
environment interfaces. These include the layout of work- 
spaces, controls, displays, human-computer dialogues, 
forms, etc. This is the phase of design where decisions such 
as the following are made: What type of display should be 
used? How many scale markers need there be? What type 
of control should be used? How much resistance should be 
included in the control? How close together should the 
switches be placed? 

One human factors technique often used to develop op- 
timized panels, workstations, and work areas is link anal- 
ysis. The purpose of link analysis is to graphically depict 
the frequency and/or criticality associated with each of the 
various interactions occurring between the operator and 
equipment and/or between one operator and another (5). The 
links that are analyzed could be eye movements between 
displays on a console, or between objects in the environment. 
Hand movements between controls are often analyzed as 
well. The objective is to modify the arrangement of the com- 
ponents to shorten the distance between components con- 
nected by frequently employed links. 

Figure 2-7 shows the controls on an underground roof 
bolting machine and the results of a: link analysis carried 
out on the bolting operation (4). The thickness of the lines 
connecting the controls indicates the relative frequency of 
hand movements between the respective controls. One as- 
pect that stands out is the long, relatively frequent link be- 
tween the boom swing and the head sump controls. 

Another tool used by human factors specialists to aid 
in interface design is the mockup. Mockups are usually, but 
need not always be, full-scale models of the equipment or 
facility. They are usually made of inexpensive materials, 
such as foam-core cardboard or plywood. The components 
are represented by actual items of hardware or by draw- 
ings and photographs of the items. Typically, various sized 
operators pretend to operate the equipment under the 
watchful eye of the human factors specialist. The specialist 
observes behavior, questions the operators, and makes 
measurements to determine things such as whether there 
is enough room for the operator to work, whether the oper- 
ator can reach all the controls and see all the displays, how 
much of the enviroment around the equipment the operator 
can see, whether there are safety hazards or bumping and 
snagging hazards, whether there will be problems getting 
into or out of the equipment, and whether the equipment 
is laid out in an optimum manner to facilitate human 
performance. 

Short of constructing full-scale mockups, evaluations 
can be made of the engineering drawings of the equipment 
and workstations by laying two-dimensional, articulated 
plastic manikins over the drawings. These manikins can 
be manipulated through typical operator movement pat- 



terns. The manikins come in various sizes that represent 
various scale models (e.g., one-tenth or one-quarter) of large 
and small people. Figure 2-8, for example, shows an inex- 
pensive front-, side-, and top-view manikin (12). A study was 




tram 
'-Boom 
swing 

L Stab jack 

Canopy 



Head 
sump 

Feed 
*- Power boost 
— Drill rotation 




Figure 2-7.— Graphic illustration of the results of a link analysis 
of a roof bolting operation (4). 




Figure 2-8.— Example of an articulated plastic manikin for 
evaluation of engineering drawings (12). (Courtesy of s.p Rogere Cop.) 



17 



made of the body dimensions of low-seam underground coal 
miners, from which plans were presented for constructing 
two-dimensional manikins representing small (5th percen- 
tile), average (50th percentile), and large (95th percentile) 
male and female miners (1). Such manikins can be used to 
uncover design deficiencies early in the interface design 
stage. They should not, however, be considered a substitute 
for a full-scale mockup evaluation. 

With the growing use of computers to aid the design 
process, it is not surprising that several systems would be 
developed to assist in the design of workstation layouts. 
Most of these were developed within a military context. 
However, one system, the crewstation assessment of reach 
program developed for the Naval Air Development Center, 
is being modified by the Bureau for use in evaluating the 
design of underground mining equipment. The Bureau's 
crewstation analysis program (CAP) is intended for use by 
original equipment manufacturers and mining companies 



for the initial design work on new machines, and to evaluate 
existing machines. 

By using CAP, a designer can define the workstation 
(controls, seat, eye position, line of sight, and head clearance 
point) in three-dimensional space, and provide dimensions 
of a sample population or an individual. CAP then proceeds 
to evaluate the workstation with respect to the accommoda- 
tion of the computer-generated test subjects. 

Most of the analysis sections of CAP require a sample 
population for testing. CAP allows the user to input either 
the actual external anthropometric measurements for one 
or more individuals directly, or to generate a sample popula- 
tion from the means, standard deviations, and correlations 
of a set of anthropometric measurements using statistical 
methods. The external measurements (fig. 2-9) for the sam- 
ple are transformed into internal link lengths and link cir- 
cumferences, and are used to create either a link-person or 
a three-dimensional manikin as shown in figure 2-9. 




Stature 




Hip 
breadth 





Foot length 



Bideltoid 
diam 



m-hand 
ngth 



Sitting, 
height 




Figure 2-9.— Three-dimensional manikin (left) produced by CAP based on external anthropometric measurement inputs (right). 



18 



It is hoped that CAP and similar systems will expedite 
the incorporation of human factors considerations in the 
design of mining equipment. The use of such systems allows 
designers to quickly and inexpensively experiment with 
alternative design concepts, refining them and testing their 
adequacy for accommodating the user population. 

Stage 5: Facilitator Design 

During this stage, the designer plans for a set of 
materials that will encourage acceptable human perform- 
ance (2). For example, preliminary selection requirements 
are developed to help insure that people with the proper 
skills and abilities are chosen to operate and maintain the 
system. The designer also identifies where instructions, per- 
formance aids, and training will be needed and best used. 
(Chapter 9 deals with the development and evaluation of 
training in the mining environment.) 

Stage 6: Testing 

The last stage of the design process is testing. The 
development of a system cannot be considered complete 
unless the system is tested and evaluated to insure that it 
meets the objectives set forth in stage 1 and does not pro- 
duce any unintended negative effects. Actually, testing 
should be conducted throughout the development of the in- 
terface and facilitator design stages. To wait until a system 
is complete, before testing it, could result in an enormous 
waste of resources. The earlier in the process problems are 
discovered, the less costly it is to correct them. 

Initially, testing is usually carried out in a laboratory 
setting. These tests are primarily concerned with assess- 
ing whether the system performs as the engineers expected. 
Human factors specialists would assess the human perform- 
ance aspects of the tests and look for potential problems in 
interface design. Ultimately, the system would be field 
tested in real-world environments using actual operators 
and maintainers. Human factors specialists would observe 
the operation and maintenance of the system, develop ob- 
jective data collection forms and surveys, and interview the 
users to assess human factors problems with the design of 
the system. 

Design and preparation for a field evaluation takes time 
and thought. Simply putting a new system or piece of equip- 
ment in a mine and returning in 6 months for opinions is 
a sure way to kill the best of systems. The test participants 
must be trained and briefed on the operation of the equip- 
ment and the purpose of the evaluation. Their cooperation 
must be solicited, and they must be made to feel a part of 
the team. Not only should their opinions of the system be 
collected, but also they must be given the opportunity to 
suggest ways of improving the system. Further, the system 
development team must be receptive to the suggestions 
made. If the system is so far along that no real changes can 
be made, regardless of the outcome of the field test, then 
one should seriously question the utility of the test and 
perhaps even the system itself. The testing stage of system 



development is of prime importance to the design process 
and not an afterthought performed merely to confirm the 
obvious. 



DISCUSSION 

As pointed out at the beginning of the discussion of the 
system design process, most things designed and developed 
by mining companies do not go through the various stages 
of design in a rigorous way; and for simple things, it is prob- 
ably not necessary. Nevertheless, the processes of defining 
what a system is to do, analyzing the tasks humans will 
do, designing the interfaces to facilitate human performance 
and safety, and field testing the system should be part of 
any design effort, no matter how small or simple it appears 
to be. The difference between designing a simple system 
and a complex system should be in the degree of formality 
and documentation required. The basic steps and considera- 
tions outlined in this chapter should be incorporated to the 
degree commensurate with the criticality and complexity 
of the system being designed. 



REFERENCES 

1. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford, D.K. Cad- 
del, K. Intaranont, S. Morrissey, and J.L. Selan. Mining in Low 
Coal. Volume II: Anthropometry (contract H0387022, Texas Tech 
Univ.). BuMines OFR 162(2)-83, 1982, 123 pp.; NTIS PB 83-258178. 

2. Bailey, R. Human Performance Engineering: A Guide for 
Systems Designers. Prentice-Hall, 1982, 672 pp. 

3. Crooks, W.H., K.L. Drake. T.J. Perry. N.D. Schwalm. B.F. 
Shaw, and B.R. Stone. Analysis of Work Areas and Tasks To 
Establish Illumination Needs in Underground Metal and Nonmetal 
Mines. Volume I of II (contract J0387230, Perceptronics, Inc.). 
BuMines OFR 11KD-81, 1980, 254 pp.; NTIS PB 81-236804. 

4. Foster-Miller Associates. Design and Develop Standardized 
Controls in Roof Bolting Machines— Preliminary Design (contract 
H0292041). BuMines OFR 107-80, 1980, 63 pp. 

5. Geer, C. Human Engineering Procedures Guide. U.S. Air Force 
Aerospace Med. Res. Lab., Wright-Patterson AFC, OH, AFAMRL- 
TR-81-35, 1981, 239 pp. 

6. Kinkade, R., and J. Anderson (eds.). Human Factors Guide for 
Nuclear Power Plant Control Room Development. Essex Corp.. San 
Diego, CA, 1983, 385 pp. 

7. McCormick, E., and M. Sanders. Human Factors in Engineer- 
ing and Design. McGraw-Hill, 5th ed.. 1982. 615 pp. 

8. Meister, D. Human Factors: Theory and Practice. Wiley Inter- 
science, 1971, 415 pp. 

9. . Behavioral Analysis and Measurement Methods. Wiley, 

1985, 509 pp. 

10. Sanders, M.S., and G.R. Kelley. Visual Attention Locations 
for Operating Continuous Miners, Shuttle Cars, and Scoops. 
Volume I (contract J0387213, Canvon Res. Group Inc. 1 . BuMines 
OFR 29(l)-82, 1981, 142 pp.; NTIS PB 82-187964. 

11. Simpson, G. and S. Mason. Design Aids for Designers: An 
Effective Role for Ergonomics. Appl. Ergonomics, v. 14. No. 3. 1983. 
pp. 177-183. 

12. S.P. Rogers Corp. (Santa Barbara. CA). ADAM. Anthropo- 
metric Data Application Mannikin. 1976, 5 pp. 



19 



CHAPTER 3.— HUMAN CAPABILITIES AND LIMITATIONS 




People are not infinitely adaptable; they have limitations. Recognition of these limitations is a step toward 
designing for increased safety and productivity. 



In chapter 2 the human-hardware environmental sys- 
tem was presented. The human as a system component was 
described as receiving information, processing it, and tak- 
ing actions based on it. These three functions will serve as 
the basis for organizing the diverse information in this 
chapter. In addition to the information reception-processing- 
.action aspects of humans, their anatomical and biological 
characteristics also impose limitations and provide capa- 
bilities that affect system effectiveness. The last section of 
this chapter will address these topics. 



WHO ARE MINERS 

There has not been much literature describing the 
characteristics of today's miners. What data exist, however, 
point toward several consistent trends that are changing, 
and will continue to change, the composition of the mining 
workforce. The first trend is that miners are getting 
younger. For example, the National Research Council of the 
National Academy of Sciences (23) 1 reports that among 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



underground coal miners, those under 30 yr of age increased 
from 20% of the workforce in 1971 to 41% by 1979. This 
trend is seen also in the superintendent and supervisor 
ranks where average ages are dropping. 

The second trend, associated with the first, is that newly 
hired miners have less mining experience than miners in 
the past. Companies do not have the substantial pools of 
experienced miners from which to select, as they did in prior 
years. 

Today's young miners are also better educated than 
miners in the past. The President's Commission on Coal 
(24) estimated that three-fourths of entering miners have 
at least a high school education, with many (one-third or 
more) having some education beyond high school. 

The proportion of female miners is also increasing. 
Reflecting the changing social climate, women are being 
hired to perform what in the past had been traditionally 
male-dominated jobs. It is estimated that women will com- 
pose 10% or more of the mining work force in the near 
future. 

These trends toward younger, more educated workers, 
and increasing numbers of women in the workforce have 
implications for training and equipment design that can- 
not be ignored. 



20 



HUMAN AS AN INFORMATION RECEIVER 

People receive information about their environment 
through their senses of sight, sound, smell, touch, and taste. 
People, however, have certain built-in limitations and 
characteristics that affect the range and amount of infor- 
mation they can receive. Only the first three senses are 
discussed in this section. 



Sight 

A simple diagram of the eye is shown in figure 3-1. Light 
enters the eye through the transparent cornea and passes 
through a clear fluid called aqueous humor. The light then 
passes through the pupil, a circular aperture whose size is 
changed by muscles attached to the iris. The iris is the part 
of the eye that gives it its characteristic color (blue, brown, 
etc.). The pupil is the black spot (actually a hole) in the 
center of the eye. The iris regulates the amount of light 
entering the pupil by enlarging (dilating) the pupil or by 
constricting it. Light rays passing through the pupil are 
refracted (bent) by the lens. The light is bent so that the 
light rays are brought to focus on the back inside surface 
of the eyeball called the retina. 

Accommodation 

The lens is adjustable in thickness to permit objects 
located at different distances to be focused on the retina. 
This focusing is done automatically by small ciliary muscles 
attached to the lens. When focusing on objects close to the 
eye, the muscles contract and cause the lens to increase in 
thickness. When viewing objects far away, the muscles relax 
and the lens becomes thinner. This process of changing focus 
is called accommodation. 

Everyone has an accommodation range; that is, the eye 
can focus objects within a given range of distances. Objects 
too close to, or too far away from, the eyes cannot be brought 
into sharp focus. The shortest distance at which an object 
can be brought into sharp focus is called the near point, and 
the longest distance is called the far point. Age has a pro- 
found effect on the power of accommodation because the lens 
gradually loses its elasticity; therefore, the near point 
gradually recedes, while the far point remains more or less 
the same. (This is why older people who become farsighted 
hold newspapers at arms' length to read them.) The average 
near point, in inches, for various ages, as given by Grand- 
jean (9), is as follows: 
16 yr..3.2, 32 yr..4.9, 44 yr..9.8, 50 yr..l9.7, 60 yr..39.4. 

The level of illumination is a critical factor in accom- 
modation. When lighting is poor, the far point moves nearer 
and the near point recedes, giving a smaller range of ac- 
commodation. Both speed and precision of accommodation 
are reduced. Contrast is also important; the more an object 
stands out against its background, the quicker and more 
precise the accommodation. This is why signs, to be readable 
at long distances, should be well lit, clean, and have high- 
contrast lettering. 

The retina is the heart of the visual process. It is com- 
posed of two types of light-sensitive receptors called cones 
and rods. There are 6 to 7 million cones concentrated in an 
area called the fovea, which is located around the optical 
axis. This is the area of maximum visual resolution. Cones 
require relatively high levels of illumination to become ef- 
fective, and therefore are used primarily for daylight vision. 



Sclerotic coat 
(sclera) 



Choroid coat 
(choroid membrane) 




Optic nerve 



Ciliary muscle 



Figure 3-1 .—Diagram Of the eye. (Adapted from reference 9. courtesy of 
Taylor and Francis Ltd.) 



In addition, cones are sensitive to differences in color and 
give rise to color vision. 

Outside of the foveal area, the concentration of cones 
drops off markedly, while the concentration of rods increases 
dramatically. Although rods are more sensitive to light than 
are cones, they do not detect fine differences in shape or 
color. They become the dominant sense receptor in poor 
illumination. 

Adaptation 

As illumination levels change, the rods and cones must 
adapt to these changing light levels. This process is called 
adaptation. With decreasing levels of illumination, sensi- 
tivity to light increases. Adaptation to darkness (dark adap- 
tation) takes a comparatively long time. Going from bright 
daylight into a dark room results in partial adaptation 
within 5 to 10 min, with full adaptation taking 30 to 60 
min. Hence, sufficient time must be given to acquire good 
night vision. 

Light adaptation is much faster than dark adaptation. 
Initial reductions of 80^ in retinal sensitivity occur in 0.05 
s, with full adaptation occurring in 1 or 2 min. The implica- 
tion of this is that, if there is a bright light in an otherwise 
dark environment, the eye will tend to adapt to that bright 
light and hence lose sensitivity for viewing the darker 
surroundings. 

There is another phenomenon (Purkinje shift) related 
to color perception that occurs as levels of illumination 
change. At high levels of illumination, the eye is most sen- 
sitive to green and yellow-green colors. As illumination 
levels decrease, however, the eye becomes most sensitive 
to blue-green colors. This is the reason that fire trucks in 
many communities are painted a greenish shade rather 
than red. 

Field of Vision 

The field of vision is that part of one's surroundings that 
can be seen when both the eyes and the head are held still. 
Figure 3-2 shows the field of vision and also indicates the 
effect of moving only the eyes, only the head, or both {12). 
This figure uses the concept of visual angle, which is illus- 
trated in figure 3-3. Figure 3-3 also presents a formula for 
computing visual angles of objects at various distances. The 
further away an object is located, the larger it must be to 
maintain a constant visual angle. Consideration of the field 



21 



of vision is important in designing equipment to help in- 
sure that needed information and displays can be seen 
without excessive head movements. 

With the eyes and head stationary, the area of distinct 
vision is only about 1' of visual angle, corresponding to the 
foveal region on the retina. Outside this area (middle and 
outer fields of vision), objects become progressively blurred 
and indistinct. In the middle field, movement and chang- 
ing contrasts or levels of illumination are noticed. Objects 
in the outer field must flicker or move to be noticed. 



15° 15° 

optimum optimum 



35° max 




40°max 



' 35°max 




15° 

optimum 

Normal line 
of sight 

15° 

optimum 



EYE ROTATION ONLY 



0° 
optimum 



65°max 



60°max 




60°max 




Normal line 
of sight 



35 max 



HEAD ROTATION ONLY 



15° 15° 

optimum y-+-»/ optimum 



90° max 



95°max 





95°max 



NORMAL LINE OF SIGHT 



15° 
optimum 

Normal line 
of sight 
15° 

optimum 



Figure 3-2.— Field of vision and effect of eye and head rota- 
tion. (Adapted from reference 9, courtesy of Taylor and Francis Ltd.) 



Visual angle 



Object 



\- Length (L) 




To compute angles up to 10° (800'): 
visua | an,,. . <L«§HU 

( L and D must be measured in the same 
units, i.e., inches, centimeters, etc.) 

Figure 3-3.— Illustration of the concept of visual angle. 



Visual Acuity 

Visual acuity is the ability to see fine detail clearly. 
Actually, there are several types of visual acuity. Minimum 
separable acuity refers to the smallest space between parts 
of a target that the eye can detect. This acuity is measured 
using the standard eye charts consisting of different letters, 
or "E's" facing different directions. Vernier acuity refers 
to the ability to distinguish the lateral displacement (or off- 
set) of one line from another such that if the displacement 
did not exist, the two lines would form one continuous line. 
Minimum perceptible acuity is the ability to detect a spot 
or dot. Stereoscopic acuity refers to the ability to differen- 
tiate two objects as being different distances from the eyes. 

In all types of visual acuity, the more peripheral a target 
is in the visual field, the poorer the acuity. The greater the 
illumination and contrast of a target, the greater will be 
the acuity. As a point of reference, under good illumina- 
tion and contrast, the normal minimum separable acuity 
is about 1 ' of visual angle (this corresponds to 20/20 vision). 

Detection of Movement 

Movement is perceived in two ways. First, a moving 
object is kept in view by moving the eyes, and the person 
receives information regarding the object's motion from the 
eye movements. In the second case the eyes are stationary, 
and the object's image moves across the retina. Under this 
condition, the minimum velocity (movement threshold) that 
can normally be detected is about 1 ' to 2 ' of arc per second. 
The movement threshold can be reduced by an order of 10 
if another stationary object is also present in the visual field. 
This has implications in underground and surface mines 
where stationary objects may not be visible at night. 

The effect of adding general background illumination, 
in addition to caplamp illumination, on the detection of mov- 
ing objects in the peripheral visual field was reported by 
Martin and Graveling (1 7). For each condition, the mean 
peripheral detection angle was computed. The results in- 
dicated an improvement in detection angle by adding only 
5 lx of background luminance. Figure 3-4 summarizes the 



Caplamp only 


' ' 


• 1 i i 
nly 


1 ' 


i i i i 


— i — r- -i i 


W/A 






5-lx backgro 


und o 


%M^ 


m. 


Caplamp plus 5 lx 




/^^^ 


V/ /ft/, 


^ 


450-lx control 










^^^ 


'W/ 


//// 


Wa 







i i i 


• i 


ii i i 


i i i i 



65 70 75 80 85 90 

MEAN PERIPHERAL DETECTION ANGLE, deg 

Figure 3-4.— Effect of caplamp and background illumination 
on detection of moving objects in the periphery of the visual field. 

(Adapted from reference 17, courtesy of Butterworth Scientific Ltd.) 



22 



results. The 9 ° increase in detection angle, achieved by add- 
ing background illumination to caplamp illumination, 
translates into an increase in the visual field of approx- 
imately 5 ft at a distance of 50 ft. 

Hearing 

Sound originates from vibrations of some source. The 
vibration causes air molecules to move back and forth, 
creating corresponding increases and decreases in air 
pressure. The sound "waves," much like the ripples caused 
by dropping a rock in a still pond, are sensed by the hear- 
ing mechanism of the ear. 

Figure 3-5 shows a diagram of the ear divided into three 
anatomical divisions: outer ear, middle ear, and inner ear. 
The outer ear consists of the pinna, which collects sound 
energy and passes it through the auditory canal to the tym- 
panic membrane (eardrum). The sound waves cause the ear- 
drum to vibrate. This vibration is transmitted through the 
middle ear by three, very small, interconnected bones or 
ossicles (malleus, incus, and stapes). The stapes is attached 
to the oval window of the cochlea. The cochlea, located in 
the inner ear, is the organ that transforms the sound vibra- 
tion into electrical impulses that are transmitted to the 
brain for interpretation. 

One point worth mentioning is that the air pressure act- 
ing on the outer ear and middle ear sides of the eardrum 
should be equal. To achieve this, there is a tube (the 
eustachian tube) that connects the middle ear to the back 
of the throat. When a person changes elevation rapidly, as 
would be the case when descending or ascending a mine 
shaft, the eustachian tube may close, and pressure may 
build up on one side of the eardrum. This differential 
pressure causes the eardrum to stretch and can be quite 
painful. In addition, the stretched eardrum cannot vibrate 
freely, and the affected person loses some of his or her sen- 
sitivity to sound. This loss of hearing can be dangerous if 
the person depends on sounds to alert him or her of danger. 
The eustachian tube can usually be opened by chewing, 
swallowing, or yawning. 

Figure 3-6 illustrates the cochlea as it would appear if 
one looked into it from the middle ear. The cochlea is filled 
with fluid, and when the stapes of the middle ear vibrate 
the oval window, a wave pattern is set up in the fluid. The 
movements of the fluid force the basilar membrane to 
vibrate, which in turn forces the small hair cells on the 
organ of Corti to brush against the tectorial membrane. This 
stimulates the hair cells, and electrical impulses are sent 
to the brain. If a person is repeatedly exposed to loud noises, 
the hair cells can be permanently damaged by hitting 
against the tectorial membrane. The actual process of how 
complex sounds are encoded in the cochlea and later inter- 
preted by the brain is still largely a mystery. Several 
theories are postulated, but none fully explains the com- 
plex processes involved. 

Sound Localization 

The position of our ears enables us to tell what direc 
tion a sound is coming from. This sort of information is ex 
tremely beneficial in the work environment. Knowing what 
direction a moving vehicle is coming from, or where the 
creaks and groans of the "working" roof are emanating 
from, can mean the difference between life and death. 

The ear uses two cues to determine the location of a 
sound. The first cue is the difference in time it takes the 



Pinna 



Oval window 
Inner ear 




Auditory 
nerve 



Cochlea 

Basilar membrane 



Round 
window 



Figure 3-5.— Illustration of principal structures of the ear. 

(Adapted from reference 18, courtesy of McGraw-Hill) 



Vestibular 

membrane 



Scala vestibuli 
(space) 



Tectorial 
membrane 



Auditory 
nerve 




Epithelial 
hair cells 



Organ 
of Corti 



Scala tympani 
(space) 



Basilar 
membrane 



Figure 3-6.— Illustration of the cochlea, looking into it from the 
middle ear. 



sound to reach each ear. A sound coming from the right side 
of the listener will reach the right ear a fraction of a second 
sooner than it reaches the left ear. The second cue is the 
difference in sound intensity reaching each ear. A sound 
from the right side of the listener is more intense in the 
right ear than in the left ear because of the shadowing ef- 
fect of the head. This is easily demonstrated by adjusting 
the relative loudness of two speakers in a stereophonic 
system. For example, increasing the loudness of the right 
speaker makes the sound appear to move across the room 
to the right. 

Accurate localization, however, occurs only when the 
sound source is situated to the right or to the left of the 
listener. If the head is fixed, front-back and up-down 
discrimination is poor. It is very important, therefore, that 
the head be free to move, allowing the person to place the 
sound source along a left-right line relative to the ears. 

There are several design features that can alter the 
ability to accurately locate sounds. If the sound is blocked 
to one ear, localization is poor. For example, if a driver keeps 
the left window of a vehicle cab down and the right win- 
dow up, sounds will appear louder in the left ear even if 
they are coming from the right side of the vehicle. (.This 



23 



same phenomenon occurs with operator cabs that are open 
on only one side.) Sound bounces off surfaces, making it ex- 
tremely difficult to localize the actual source. This kind of 
problem is especially acute in underground mines. Finally, 
if a person has a differential hearing loss in one ear relative 
to the other, his or her ability to localize sounds will be 
impaired. 

Tone and Loudness Discrimination 

In the work environment, it is necessary to discriminate 
between sounds in terms of tone (actually frequency) and/or 
loudness (intensity). The loudness and tone of roof "talk" 
can serve as an alert to an impending roof fall. Motor noises, 
if correctly identified, can indicate mechanical problems. 
Two types of discrimination can be defined. The first type 
is a relative judgment in which there is an opportunity to 
compare two or more stimuli to determine which is louder, 
higher pitched, or simply whether they differ. The second 
type is an absolute judgment in which no opportunity ex- 
ists for comparison. In essence, one must compare the sound 
to a sound one remembers hearing. In most work situations, 
discriminations are absolute judgments. Unfortunately, the 
ability of people to make absolute discriminations between 
individual stimuli is not very great. In this connection, 
reference 21 referred to "the magical number seven, plus 
or minus two" (i.e., five to nine) as the number of absolute 
discriminations people can make along a single dimension. 
Thus, one would expect that people can discriminate five 
or six sounds of different loudness or different tone. If dif- 
ferent dimensions are combined (e.g., loud and soft inten- 
sity with high and low frequency), the number of absolute 
judgments can be increased tenfold or more. 

Masking 

The major limitation of the ear is its relative inability 
to detect a signal in a noisy environment. When this occurs, 
the signal is said to be masked by the noise. Masking will 
be further discussed in chapter 8. 

Effect of Age on Hearing 

As one advances in age, hearing sensitivity declines. 
The effect is greater for higher frequencies than for lower 
frequencies. Figure 3-7 shows the deterioration in hearing 
threshold with age for 1,320 underground coal miners (11). 
As can be seen, the major loss of sensitivity occurs with fre- 
quencies above 3 kHz (3,000 Hz). It is at frequencies above 
3,000 Hz that important speech sounds are contained. Thus, 
with advancing age, speech comprehension declines. The 
presence of masking noise makes the situation even worse 
for older individuals. It should be pointed out that the hear- 
ing loss pattern observed in the miner population shows lit- 
tle difference from that of nonminer populations (11). 

Smell 



CD 

■o 

en 
c/> 
o 

_i 

e> 

z 

< 
UJ 

I 






1 I 1 II 1 III 
— Aoft 




^^^^ \<J8-24 


10 


— ~~ — V *"^^\ >v 




^^v \ V25-34 


20 


\v \ \^35-44 


30 


\\V^ 




\ V-45-54 


40 


\ v^ 




y- 55-64 


50 


\z. 


en 


Ill 1 1 1 1 III 



0.5 I 2 3 

FREQUENCY, kHz 



4 5 6 



Figure 3-7.— Changes in hearing sensitivity with age for 1 ,320 

Underground COal miners. (Adapted from reference 1 1 , courtesy of National In- 
stitute for Occupational Safety and Health) 



(e.g., coffee, paint, banana, etc.). With respect to identify- 
ing odors in terms of intensity only, about four different 
levels can be identified. Another limitation of the sense of 
smell is that a person adapts to an odor rather rapidly and 
soon becomes unaware of its presence. 

Many U.S. metal mines use a stench system to alert 
miners of an emergency; a foul-smelling substance is re- 
leased into the ventilation system. As will be discussed in 
chapter 5, the selection and design of such systems are in- 
fluenced by the limitations of the olfactory sense. 



HUMAN AS INFORMATION PROCESSOR 

In order to process information, three functions must 
be present: (1) memory, the ability to store information; (2) 
decisionmaking, the ability to evaluate alternatives and 
select a course of action; and (3) attention, the ability to at- 
tend to environmental features and numerous sources of 
information. 



The sense of smell is relied on to provide information 
about hazardous things in the work environment such as 
spilled or leaking chemicals, dangerous fumes, or the 
presence of fire. The sense organ for smell is a small 2- to 
3-in 2 patch of cells located in the upper part of each nostril. 
A sense of smell is not very good when it comes to making 
absolute identifications of specific odors. Untrained 
observers can identify approximately 15 to 32 common odors 



Memory 



\ 



Human memory can be conceptualized as consisting of 
two components, a working memory and a long-term 
memory. 

Working memory receives inputs from sensory channels 
(eyes, ears, etc.) and stores a coded representation of that 



24 



information. A characteristic of working memory is that in 
the absence of attention, information will degrade, and any 
operations performed with this information will deteriorate. 

The fragile nature of working memory can be easily 
demonstrated. Ask someone to remember three random let- 
ters (e.g., ZBL) while counting backwards by threes from 
a given number (e.g., 834). After about 20 s of counting 
backwards, ask the person to recall the letters. It is doubt- 
ful whether he or she will be able to do so. The reason is 
that the act of counting backwards prevents a person from 
paying attention to the letters in working memory; that is, 
it prevents rehearsing the letters. This same phenomenon 
occurs when an instruction is given to an employee, and 
before the instruction can be carried out, the employee is 
distracted or receives other instructions. Without time to 
encode and rehearse the instruction, it is very likely that 
it will be forgotten. 

Working memory also has a finite capacity for holding 
information. It is generally recognized that the limit is 
seven, plus or minus two (i.e., five to nine) pieces of unre- 
lated information. This means that, from working memory, 
people can recall five to nine unrelated digits, five to nine 
unrelated words, or five to nine unrelated sentences. If 
materials can be grouped into meaningful "chunks," then 
more items can be recalled. But again, people would be ex- 
pected to recall only five to nine chunks. For example, ask 
someone to recall the letter string FB-IJF-KTV. If the let- 
ters are grouped into meaningful chunks, the task is much 
simpler; i.e., FBI-JFK-TV. For remembering letters and 
digits (e.g., equipment part numbers), the optimum size of 
a chunk appears to be three to four items. Errors can be 
reduced if part numbers or numeric codes are divided into 
optimum sized chunks. For example, a designation such as 
834-431-212 is better remembered than 8-344132-12. 

Some tasks involve receiving or processing a continuous 
sequence of stimuli. An operator must make a different 
response to each stimulus or series of stimuli, and he or she 
is not expected to remember the entire string. Most equip- 
ment operations are of this sort where a constantly chang- 
ing sequence of stimuli require different responses. This 
situation is called a running memory task. If an operator 
is asked to recall the last few stimulus items, the memory 
span will be much smaller than five to nine items, and is 
often no more than two prior items. When trying to recon- 
struct an accident scenario, it is common for the people 
watching the sequence of events to be unable to recall what 
actually happened. (Often, what they relate is what they 
think should have logically happened, which may or may 
not be what actually happened.) 

Long-term memory is vast, yet imperfect. No computer 
in existence can store as much information as is contained 
in the long-term memory of an average adult. The problem 
is that much of what is learned is forgotten and much of 
what is recalled was never learned. What ultimately is 
stored in long-term memory must first be stored in work- 
ing memory where it is coded and organized for effective 
storage in long-term memory. This coding and organization 
requires that attention be paid to the information in work- 
ing memory. 

Methods for organizing and coding information can en- 
hance long-term memory. For example, one method called 
the method of loci is useful for remembering a list of se- 
quential items (tasks to perform, instructions to follow). The 
idea is to attach the items to a spatial map in memory. The 
first step is to picture a sequence of actions that are per- 
formed daily; for example, your coming to work. You form 



a mental map; that is, you picture the sequence of events 
and their location in your mind. You enter the company 
gate, park the car in the parking lot, walk to the change 
room, change clothes, get a cup of coffee at the coffee 
machine, read the bulletin board, etc. The next step is to 
tie each thing you need to remember to a location on your 
mental map. This is done by visualizing the thing you need 
to remember at that location. If the visual images are 
bizarre, the sequence of things will be easier to remember. 
When the items need to be recalled, you have only to men- 
tally traverse your route to work and recall each chunk of 
information stored at each location. With practice, this 
technique is very effective because it uses visual imaging 
to organize information in long-term memory. 

Decisionmaking 

Decisionmaking is a complex process by which people 
evaluate alternatives and select a course of action. This 
process involves seeking out information, estimating prob- 
abilities of outcomes, and attaching values to the potential 
outcomes. Examples of common types of decisions include 
deciding what make and model of haulage truck to buy, 
deciding whether to set a temporary roof support before 
checking the integrity of the roof, deciding what caused an 
electrical malfunction in a piece of equipment, and deciding 
whether to come to work in the morning. 

Unfortunately, people are not optimal decisionmakers 
and often do not act "rationally;" that is, they do not act 
according to objective probabilities of gain and loss. There 
are a number of biases inherent in the way people seek in- 
formation, estimate probabilities, and attach values to out- 
comes, and these biases produce what, to some, may appear 
to be irrational behavior. The following is a short list of 
some of these biases (33) 

1. People give an undue amount of weight to early evi- 
dence or information. Subsequent information is considered 
less important. 

2. People are generally conservative and do not extract 
as much information from sources as they optimally should 
extract. 

3. The subjective odds in favor of one alternative or 
another are not assessed to be as extreme nor given as much 
confidence as they optimally should be given. 

4. As more information is gathered, people become more 
confident in their decisions, but not necessarily more ac- 
curate. For example, people engaged in troubleshooting a 
mechanical malfunction are often overly confident that they 
have entertained all possible diagnostic hypotheses. 

5. People have a tendency to seek far more information 
than they can adequately absorb. 

6. People often treat all information as if it were of equal 
reliability, even though it is not. 

7. People appear to have a limited ability to entertain 
more than a few (three or four) hypotheses at one time. 

8. People tend to focus on only a few critical attributes 
at a time and consider only about two to four possible choices 
that are ranked highest of those few critical attributes. 

9. People tend to seek information that confirms the 
chosen course of action and to avoid information or tests 
whose outcome would contradict the chosen course of action. 

10. A potential loss is viewed as having greater conse- 
quence, and therefore exerts a greater influence over deci- 
sionmaking behavior than does a gain of the same amount. 

11. People believe that mildly positive outcomes are more 
likely than are mildly negative outcomes, but that highly 



25 



positive outcomes are less likely than are mildly positive 
outcomes. 

12. People tend to believe that highly negative outcomes 
are less likely than are mildly negative outcomes. 

These biases explain, in part, why some workers will 
engage in obviously dangerous behaviors to get a job done 
faster or with less effort. These people do not perceive the 
probability of serious injury to be as high as it might actu- 
ally be, but are certain that they will gain by reducing the 
time and/or effort required to do the job. They also tend not 
to seek information that would contradict their perceptions 
of the situation. 

Attention 

Attention in human information processing is used in 
two different ways. The first is as a searchlight in which 
various features of the environment are attended. In some 
situations, one aspect or task must be attended and other 
distracting stimuli ignored; this is called focused attention. 
In other situations, numerous sources of information or 
multiple tasks must be attended; this is called divided at- 
tention. In both cases humans have limitations. Distractions 
are caused by irrelevant stimuli, or not everything can be 
attended, thereby important information, is missed. Under 
stress or high levels of arousal (e.g., during an emergency), 
fewer sources of information are attended, concentration 
is given those thought most important. 

A special problem related to maintaining attention oc- 
curs when operators must perform a monotonous, repetitive 
task, yet stay alert to infrequent but critical events. This 
type of situation is called a vigilance task. The classic ex- 
ample is a control room operator who monitors dials and 



displays for hours on end, waiting for something to go 
wrong. As time passes, the probability increases that the 
operator will miss a signal or critical event. This inability 
to maintain alertness is evident after the first 30 min. This 
decrement is made worse if the operator is tired, or the task 
is performed in an unfavorable environment of high tem- 
perature and humidity. It was recognized (19) that surface 
mine haulage-truck drivers work in a situation that is con- 
ducive to a decrement in vigilance performance. The load- 
haul-dump-return cycle is highly repetitive, and little 
stimulation is received from driving in circles in an open- 
pit mine (fig. 3-8). This lack of alertness makes the driver 
unable to quickly respond to an unexpected situation and 
more likely to make inappropriate actions to maintain the 
truck on the roadway (e.g., steering corrections). 

The second use of the term "attention" is as a resource. 
When performing any task, different mental operations re-' 
quire some amount of a person's limited processing resource. 
Doing more than one task at a time (e.g., divided attention) 
requires more resources than doing a single task. Atten- 
tion, as a resource, is required to keep information in work- 
ing memory, to obtain information from environmental 
sources, and to perform mental operations on that informa- 
tion. It is in this sense that attention is the "glue" that holds 
the entire information-processing function together. 

In general, the more similar two tasks are, the more 
they compete for the same resources and the greater the 
interference. It is much harder to read two different mes- 
sages at the same time than it is to read one and listen to 
the other. The more difficult the tasks, the greater the de- 
mand on resources, and the less efficient is the ability to 
do both tasks at the same time. A trolley operator can drive 
the trolley and easily converse with a dispatcher on a 







Figure 3-8.— The load-haul-dump-return cycle in surface mining creates a situation highly conducive to lapse 
in attention and alertness. 



26 



straight, clear track. As the operator goes through intersec- 
tions, multiple switches, or dangerous sections of track, 
however, his or her conversation with the dispatcher will 
deteriorate. 

Mental workload is a concept that relates to the dif- 
ference between the attentional resources available and the 
demands placed on those resources by the tasks being per- 
formed. Hence, mental workload can increase if an oper- 
ator's capacity is reduced or if task demands are increased. 
There have been numerous studies aimed at developing 
measures of mental workload, including subjective evalua- 
tions of workload, physiological measures, and performance 
measures. Although many seem promising, no single 
measure has emerged as the standard, nor is this likely to 
happen. Mental workload appears to be a multifaceted con- 
cept that probably cannot be adequately captured by a 
single measure. 



HUMAN AS ACTION TAKER 

When humans react to stimuli by making responses, 
they are concerned with the speed with which the response 
is made and the accuracy of that response. Response time 
can be divided into two components: reaction time and 
movement time. Reaction time is the time from onset of a 
stimulus to initiation of a response. Movement time is the 
time from initiation of response to completion of the re- 
sponse. For example, a person stepping into the path of a 
vehicle would be a stimulus to the driver of that vehicle. 
The driver must sense the stimulus, process the informa- 
tion, and select a response (e.g., turn the wheel or hit the 
brake). These activities take time and constitute reaction 
time. The driver must then execute the action, e.g., lift his 
or her foot and depress the brake pedal. The time required 
to lift the foot, move to the brake, and depress the brake 
would be the movement time. 

Reaction Time 

Reaction time is influenced by numerous factors. To 
organize the discussion of some of the more important ones, 
reaction time will be divided into three components: stim- 
ulus reception time, processing time, and response selec- 
tion time. The overall mean reaction times of coal miners 
to a stimulus light was found to be 0.259 s (3). The coal 
miners were alerted before the light came on, and hence, 
this value probably represents the lower bound estimate 
for overall reaction time to a simple stimulus among miners. 
Under more realistic conditions, however, reaction times 
can be 10 times as long. 

Stimulus Reception Time 

The time it takes to perceive a stimulus depends only 
slightly on the sense modality (seeing, hearing, touching, 
etc.), but depends heavily on the intensity of the stimulus. 
Auditory and touch reaction times are approximately 0.15 
s; vision and temperature reaction times are 0.2 s; smell 
reaction time is 0.5 s; and pain and task reaction times are 
1.0 s. 

For visually presented stimuli, the location in the field 
of vision is also an important determinant of reaction time. 
Reaction time is much faster to stimuli in the line of sight 
than it is to stimuli located in the periphery of the visual 
field. Anything that can make the stimulus more conspic- 



uous, such as increased size, brightness, contrast, and dura- 
tion, will decrease reaction time. Flashing lights are also 
responded to faster than are steady lights, especially if they 
are located in the periphery of the visual field. 

Processing Time 

Once a stimulus is received, it must be processed and 
a decision made to respond or not to respond to it. A major 
variable affecting processing time is the temporal uncer- 
tainty of the stimuli; that is, if a person knows when a 
stimulus will occur, reaction time is faster. For example, 
one study found that reaction time for braking an auto- 
mobile in response to an anticipated auditory stimulus was 
0.54 s, while braking in response to an unanticipated stim- 
ulus was 0.73 s (15). Another factor that influences process- 
ing time is whether a person is engaging in another task 
that could compete for attentional resources. In one study 
(26), reaction times of up to 2.5 s were found for responding 
to warning lights in the periphery while simultaneously per- 
forming a tracking task. This is very close to the results 
obtained by Summala (27), wherein the steering response 
to the onset of a light at the side of the road was measured. 
Subjects were not aware that they were in an experiment 
and were totally unexpectant of the stimulus. The average 
steering response (toward the center of the road) started less 
than 2 s after the onset of the light, reached its halfway 
strength at 2.5 s, and reached its maximum response at a 
little more than 3 s. Thus, reaction times in the operational 
environments should not be expected to be less than 2.5 s, 
and design should probably be for reaction times of 3.0 s. 
A haulage truck, for example, going 20 mph will travel 
about 90 ft in 3 s. 

Response Selection Time 

Once a stimulus has been processed, an appropriate re- 
sponse must be selected. The more choices available to a 
person, the longer the reaction time. Figure 3-9 shows the 
results of one study (5) that measured reaction time as a 




2 3 4 5 6 7 
CHOICES 



S 



Figure 3-9.— Reaction time as a function of the number of 

response Choices available. (Based on data presented s> Dame- s 



27 



function of the number of choices available. Another 
variable that is important is whether a response is compati- 
ble with a stimulus. The more compatible a response is' to 
a stimulus, the faster the reaction time. (Compatibility is 
discussed in more detail in chapter 6.) 



or tapping. Probably the most important aspect of repetitive 
movements is that such work requires pauses from time to 
time, and it is difficult to maintain a constant rhythm over 
time without rest breaks. 



Movement Time 

Factors affecting movement time include the distance 
traveled, direction and type of movement, load being moved, 
and type of action taking place at the end of the movement. 
It has been estimated (32) that a minimum movement time 
of about 0.3 s can be expected for most control activities. 
If one adds this time to the simplest reaction time of about 
0.2 s, the minimum control activation time (reaction plus 
movement time) is approximately 0.5 s. 

Generally, horizontal hand movements are faster than 
vertical hand movements, and continuous curved motions 
are faster than abrupt direction changes. Movement time 
is not linearly related to distance traveled because higher 
movement velocities (inches per second) can be attained 
with longer movements than with shorter movements. 
Generally, reaction time using the hand is approximately 
20% faster than using the foot, and the preferred hand is 
approximately 3% faster than the nonpreferred hand (14). 
These sorts of considerations, of course, have implications 
for the layout of equipment controls where speed of opera- 
tion is critical. 



Movement Accuracy 

Several types of movements can be distinguished: posi- 
tioning movements, continuous movements, and repetitive 
movements. 



Positioning Movements 

Reaching for something or moving an object to another 
location are examples of positioning movements. Accuracy 
of blind positioning movements was assessed by Fitts (7), 
and the results indicated that people are most accurate in 
blind positioning if a target is straight ahead. Accuracy 
decreased as the target moved to more peripheral positions 
and was better for targets at and below shoulder height than 
for those above shoulder height. In many mining situations, 
operators are required to reach for a control without look- 
ing at where they are reaching. To avoid groping or con- 
tacting the wrong control, controls that will be operated 
blindly should be placed in front of the operator, at a below- 
shoulder height. 

Continuous Movements 

Continuous movements require accurate control over 
the entire movement, as for example in drawing a line on 
a piece of paper. One study of tremor in arm movements 
(20) found that tremor was significantly greater (four to six 
times) if the arm movements were in-out (away from-toward 
the body) than if they were up-down or right-left. 

Repetitive Movements 

Repetitive movements involve successive performance 
of the same action over and over, such as in crank turning 



ANATOMICAL CHARACTERISTICS 

It is no surprise to anyone that human bodies come in 
a variety of sizes and shapes. The science of measuring body 
dimensions is called anthropometry. Anthropometric data 
are essential for designing equipment and workspaces that 
will accommodate the worker population. Anthropometric 
data include body dimensions and range of movement. 
Before presenting some of the basic anthropometric data, 
a review of some basic concepts and some of the limitations 
of using such data is given. 

Percentiles 

Anthropometric data are usually reported as percen- 
tiles; e.g., the 95th percentile standing height for male low- 
seam coal miners is 73.7 in. Percentiles indicate the percen- 
tage of a particular population that have values less than 
the value given. Thus, it is known that 95% of male low- 
seam coal miners are less than 73.7 in tall and 5% are 73.7 
in or taller. The most commonly reported percentiles are 
the 5th, 50th, and 95th. The 5th percentile value is the small 
person, as only 5% of the population have values smaller 
than the 5th percentile value. The 50th percentile value 
represents the "average" person; half the population have 
values less than the 50th percentile value and half have 
values equal to or greater than the 50th percentile value. 
The 95th percentile value, of course, represents the large 
person. 

When equipment or workstations are designed, they are 
usually designed for the 5th to 95th percentile values, that 
is, the middle 90% of the population. The reasons for this 
is that accommodation of the extreme 5% at each end of a 
distribution requires a disproportionate range of adjusta- 
bility in a workspace. For example, the 5th to 95th percen- 
tile sitting height spans a range of 4.2 in. The 1st to 99th 
percentile sitting height, however, spans a range of 6.0 in. 
Therefore, to accommodate the extra 10% of the population, 
vertical seat height adjustment would have to be increased 
almost 43%. 

Fallacy of the "Average" Person 

The term "average size" is often used, but in reality no 
one is average on more than one or two body dimensions. 
That is, a person who is average in overall standing height 
may have short legs and a long upper torso, or long legs 
and a short upper torso. Short people may have long arms, 
and tall people may have short arms. In a classic study (10), 
not a single person among 4,000 Air Force men could be 
found within ±30% of the mean on 10 body dimensions. 

The fact that the smallest person is not necessarily the 
smallest on all dimensions, that the average height person 
is not necessarily the average on all dimensions, and that 
the largest person is not necessarily the largest on every 
dimension has important implications for using anthro- 
pometric data in design. First, one cannot simply add 
dimensions together and expect to arrive at the correct 
percentile value. For example, adding the 5th percentile 



28 



fingertip-to-elbow length to the 5th percentile elbow-to- 
shoulder length will not yield the 5th percentile fingertip- 
to-shoulder length. The correct procedure is more com- 
plicated, requires additional information, and is beyond the 
scope of this report. 

Second, if individual dimensions are used to design 
workspaces, a larger proportion of the population will be 
excluded than would be expected. For example, if an oper- 
ator's compartment was designed so that hand controls and 
foot controls could be reached by the 5th percentile person, 
more than 5% of the population would not be able to reach 
either the foot controls or hand controls, or both. The reason, 
of course, is that the 5% excluded from reaching the foot 
controls are not necessarily the same 5% excluded from 
reaching the hand controls. If several individual 5th and 
95th percentile dimensions are used, the proportion of the 
population that would be excluded could be over 50%. 

Other Limitations of Anthropometric Data 

There are two classes of anthropometric data: static and 
dynamic. Static anthropometric data are collected on sub- 
jects who assume erect, rigid postures and are wearing no 
clothes or only the minimum required for modesty. These 
postures are not often those actually assumed in the work 
environment. People do not sit erect when operating equip- 
ment. Arm length is not an accurate measure of reach dis- 
tance because it does not take into consideration extending 
the shoulder, bending the waist, and twisting the torso. 
Thus, one must be careful in applying static anthropometric 
data to designing a real workplace. Dynamic anthropo- 
metric data take into account normal work postures and 
the interaction between body parts that affect movements 
and reaches. Unfortunately, there are far less dynamic data 
available than there are static data. 

Virtually all static anthropometric data are collected 
on people clothed in less than normal working attire. Winter 
garments, gloves, heavy boots, etc., are usually not worn 
when the measurements are taken. The designer, therefore, 
must increase dimensions to accommodate any additional 
clothing and any restriction in movement caused by the 
wearing of such clothing. 

There is an enormous amount of static anthropometric 
data available on all sorts of populations, including truck 
drivers, coal miners, and flight attendants. By far, the most 
comprehensive data base is from the military. The impor- 
tant point is that there can be systematic differences in body 
dimensions between different occupational groups. For ex- 
ample, underground low-seam coal miners were measured 
and the results were compared with those of military per- 
sonnel and long-distance truck drivers (2). The results 
showed that male miners were significantly heavier and 
tended to have larger circumferences of the torso, arms, and 
legs than did the comparison populations. The miners, 
however, did not differ reliably from the comparison groups 
in terms of linear dimensions (i.e., height, arm length, leg 
length, etc.). Female low-coal miners were found to have 
larger shoulder, waist, biceps, and thigh circumferences 
than did the comparison populations, but again linear 
dimensions did not differ. 

It is important, therefore, that the designer choose a 
data base that closely represents the worker population for 
which he or she is designing. Based on Ayoub (2), it seems 



safe to use military personnel data for most design prob- 
lems, keeping in mind the increased circumferences for 
miner populations. 



Static Anthropometric Data 

Appendix A contains static anthropometric data for 
male and female military populations (30). In using the data 
for mining applications, one must keep in mind its limita- 
tions. Allowances must be made for clothing, including 
heavy jackets, hardhats, battery packs and self-rescue units 
(for underground miners), and boots. Standing and sitting 
heights will be increased, and clearance spaces will have 
to be enlarged to accommodate the added bulk from clothing 
and personal protective equipment. The data in appendix 
A, therefore, should be considered as estimates and used 
as rough indicators for equipment and workspace design. 

Range of Movement 

The human body is not infinitely flexible. Joints impose 
limits on the range of movements possible— elbows pivot in 
one direction only but shoulder joints can rotate in all direc- 
tions. The range of a joint movement is measured in degrees 
of angular motion. Appendix B contains data on common 
joint movements, including the 5th and 95th percentile 
range of movement for both males and females (32). The 
data are based on college-aged subjects. From ages 20 to 
60, the decline in range of movement is only about lO^r . 

Reach Envelopes 

The combination of joint mobility and anthropometric 
dimensions define the envelope within which a person can 
reach objects. In addition to mobility and anthropometrics, 
the posture assumed by a person, the clothes worn, and the 
actual manipulative task to be performed influence the 
reach envelope. For example, the more reclined the sitting 
posture, the shorter the arm reach envelope in the forward 
direction. If a person simply has to activate a pushbutton 
with his or her fingertips, the reach envelope will be 2 to 
3 in. longer than if a knob must be grasped. A hand-grasp 
manipulation reduces the reach envelope an additional 2 
to 3 in (4). A winter jacket, zipped up, can also reduce reach 
envelopes by 2 to 3 in (25). 

Figure 3-10 shows a representative three-dimensional 
reach envelope (18). Several hand positions were used to 
generate the data. The cross-hatched areas represent those 
areas that were reached by all hand motions studied (6). 

In addition to reaching controls with the arm, the foot 
is also used to activate controls. Foot-reach envelopes are 
much more constraining than are arm-reach envelopes. 
Figure 3-11 shows optimal and maximal vertical and for- 
ward pedal-reach envelopes for seated operators (28). The 
data assume a horizontal seat pan and pedals that do not 
require excessive force for activation. If high levels of force 
are required, the pedals should be moved closer to the seat 
reference point, the point of intersection of the centerline 
of the seat back and the centerline of the seat pan. The max- 
imum areas indicated in figure 3-11 require quite a bit of 
thigh and/or leg movement and hence should be avoided 
for frequently used pedals. 



29 



TOP 


_Ti§^=. ^>^ T 


T|gj \ T 


-imm-J-2 



FRONT 


7 / \ \ 


i m ¥y. I= 


\ ■" 2§ t 


^— i^ ^^.2 





SIDE 











'"V 


\ 












\ 










TV 










f l) 


V^ 


1 


% 


h— ™ 


.«• 


W 



Note: Grid lines represent 6 in 

Figure 3-10.— Arm reach envelope for movements using a 
number of hand-grasp positions in three-dimensional space 
(cross-hatched areas depict regions reached under all conditions 

Studied). (Adapted by McCormick and Sanders (73) from reference 6, courtesy of 
McGraw-Hill) 



Strength 

Strength is defined as the maximal force muscles can 
exert isometrically (against a fixed object) in a single, volun- 
tary effort ( 16). The measured strength depends on the in- 
trinsic muscle strength of a person, as well as the person's 
motivation and the specific instructions given the person 
as to how to exert the force. Figure 3-12 presents 5th percen- 
tile arm strength data for four directions of motion at five 
arm positions (13). As can be seen, pull-and-push movements 
are strongest, and up-and-down movements are weakest. 

Strength data are important to designers so that con- 
trols and manual tasks are not designed to require more 
force than can be exerted by workers. Traditionally, 5th 
percentile values are used for design standards to insure 
that a task can be performed by 95% of a population. 

Strength is related to age and sex. Maximum strength 
is reached in the middle to late twenties and declines slowly 
but continuously from then on. At age 65, strength is about 
75% of what it was in the prime years. Women generally 
have less muscle strength than men. Overall, women's 
strength is about 66% of that of men; the exact percentage, 
however, is dependent on the specific muscle group meas- 
ured and ranges from 50% to 80%. 

It is important to keep in mind that most muscular ac- 
tions relevant to a job require the integrated exertion of 
many muscle groups. For example, pushing a pedal requires 
turning the ankle and extending the knee and hips, while 



15 



-i r^n r— 

Maximum area for 
-• — Toe -operated controls 
-a — Heel -operated controls 



I 

Near high 
toe 



Far high 
toe " 




KEY 
Optimum area for 

- Toe-operated controls 

— Heel-operated controls 




Floor 



25 30 35 40 45 50 15 20 25 30 35 
DISTANCE FORWARD OF SEAT REFERENCE POINT, in 



45 



Figure 3-11.— Foot reach envelopes for various types Of pedal operations. (Adapted by McCormick and Sanders (78) from reference 6, courtesy of 
McGraw-Hill) 



30 




► Push 




60 90 120 150 180 

ELBOW ANGLE, deg 



Figure 3-12.— Arm strength data. Shown are 5th percentile values for four directions of movement (up, down, pull, push) at five 

arm positions. (Adapted by McCormick and Sanders (18) from reference 13, courtesy of McGraw-Hill) 



stabilizing the pelvis and trunk on the seat. Reference 25 
collected the maximum forces that truck drivers could exert 
on pedals and the maximum torque that could be exerted 
on a 22-in-diameter steering wheel. Figure 3-13 summarizes 
the data as a function of time. Drivers were told to hold their 
maximum exertion for 15 s. 

Endurance 

Endurance refers to the ability to continue exerting a 
force over time. Unfortunately, the ability to hold maximum 
forces is rather limited. The higher the force applied, 
relative to the maximum force possible, the shorter the en- 
durance time. Maximum exertions can only be held for a 
few seconds, but an exertion that is 25% of maximum can 
be held for several minutes. This relationship is shown in 
figure 3-14. Reference 25, for example, found that the mean 
maximum force dropped 12% to 15% in just 5 s, and after 
15 s had decayed 21% to 24%. 

Circadian Rhythms 

The human body, contrary to popular belief, does not 
maintain an utterly constant, homeostatic internal environ- 
ment. It is now generally accepted that there are regular, 



significant fluctuations througout the day in almost every 
physiological measure. These fluctuations take on a rhythm 
that repeats roughly each day, and therefore the term "cir- 
cadian rhythms" has been coined to describe them. (The 
term "diurnal rhythms" is also used.) 

One of the more easily measured circadian rhythms is 
that of body temperature. Body temperature does not re- 
main constant at 98.6° F, but fluctuates about 1 ° F through- 
out the day. Figure 3-15 shows the typical temperature cir- 
cadian rhythm with the minimum value occurring in the 
early hours of the morning, followed by a pronounced rise 
over the early working hours, with a slower rise over the 
rest of the day, and finally reaching a peak in the early 
evening. 

These biological circadian rhythms are internally reg- 
ulated, but can be influenced by the external environment. 
For example, the temperature rhythm can be shifted by 
altering the sleep-wake cycle. The important fact about 
these circadian rhythms is that they are correlated with 
performance. For simple perceptual and motor skills, per- 
formance closely follows the body temperature rhythm, with 
lower performance between midnight and 8:00 a.m. and 
peak performance in the late afternoon and early evening. 
Tasks that show this cycle include visual scanning tasks 
where a person is searching for targets (e.g., the type of task 



31 



300 



£ 200 



T 



95th percentile 



50th percentile 




5 th percentile 



99.68 




Max 



5 10 

TIME,s 



Figure 3-13.— Maximum force exerted on a foot pedal and max- 
imum torque applied to a 22-in-diameter steering wheel by truck 

drivers. (Adapted from reference 25) 




4 6 

TIME,min 



Figure 3-14.— Endurance time as a function of the force main- 
tained (16). (Copyright 1970, by the Human Factors Society, Inc., and reproduced 
by permission) 




98.60 



12 2 4 6 8 10 12 2 4 6 8 10 12 

t- am. 14- p.m. H 

TIME 

Figure 3-15.— Typical circadian rhythm for body temperature. 

(Adapted from reference 22, copyright 1983, by John Wiley & Sons Ltd., and reprinted by 
permission) 



a haulage truck operator would perform); physical tasks 
such as manual materials handling; and reaction time 
tasks. It was found by Monk and Folkard (22), however, that 
tasks involving high working memory loads show a very 
different time-of-day trend. These sorts of tasks would in- 
clude immediate recall of materials presented as prose (as 
in a book). In the case of these tasks, performance declines 
over the normal working day, with poorest performance in 
the early evening— almost the exact opposite of that found 
for simple perceptual motor tasks. This indicates that dif- 
ferent biological clocks may be involved with these two 
types of functions. 



Physiological Adjustment 

When people alter their sleep-wake patterns, as when 
they change work shifts, the circadian rhythms slowly ad- 
just to the new schedule. This process of adjustment takes 
a considerable amount of time, up to 12 days in the case 
of the temperature rhythm. However, it does not take much 
time to readjust the temperature rhythm to a normal day- 
wake, night-sleep pattern. This readjustment can occur in 
1 or 2 days. There is evidence that the biological clock 
related to simple perceptual motor performance adjusts to 
change slowly, while the clock related to complex mental 
activity changes rapidly. 



32 



Shift Work 



DISCUSSION 



Circadian rhythms impose certain biological limitations 
on performance. These limitations are most important in 
the context of shift work. It was reported by Tasto and Col 
ligan (28) that 30% of miners were shift workers. Among 
metal miners, the percentage on late shifts (second or third) 
was approximately 40%. 

Three basic types of shift schedules can be distinguished: 

(1) permanent, where people always work the same shift; 

(2) rapidly rotating, where people never have more than one 
or two shifts in a row before changing to a different time; 
and (3) slowly rotating, where people work one shift for a 
week or more before changing. There seems to be two 
schools of thought with regard to which system is preferred. 
One school of thought advocates permanent shifts to max- 
imize physiological adjustment. To be effective, however, 
the workers must maintain their sleep-wake habits during 
their days off. The second school of thought advocates rap- 
idly rotating shifts so that no adjustment of the rhythms 
occur. It is believed that the constant adjustment and re- 
adjustment in permanent shift workers who revert to a nor- 
mal day shift during their days off is more harmful than 
if they work a few days totally out of synchronization with 
their circadian rhythms. The disadvantages of this approach 
are (1) night-shift performance involving simple perceptual 
motor skills will be impaired; and (2) a sleep debt may 
quickly build up, thus requiring 2 or 3 days off after each 
short run of night work. It should be pointed out that if the 
work at night involves complex memory and mental proc- 
essing tasks, a rapidly rotating shift would result in better 
performance than a permanent shift schedule because per- 
formance on such tasks is best when out of synchronization 
with the circadian rhythm. 

With respect to mining, most tasks are probably of a 
simple perceptual motor nature. For example, field studies 
of shift work performance have found that error frequency 
in reading meters (2), in nodding off while driving (22), and 
in train drivers missing warning signals (8), is higher on 
night shifts than it is on day shifts. Permanent shift sched- 
ules would probably be best under such conditions, given 
that workers try to maintain their sleep-wake patterns dur- 
ing their days off, and that adequate sleep is obtained. It 
should be pointed out that none of the experts endorse a 
slowly rotating shift system. This is considered the worst 
of both worlds. 

The major detrimental effects of shift work are sleep 
loss, disruption of social and family life, and increased 
gastro-intestinal problems. It must be pointed out, however, 
that not all studies are unanimous on these disadvantages. 
Some report advantages of being home during the day with 
family, and some report no gastro-intestinal problems. Sleep 
loss, however, appears to be fairly common. As with so many 
situations, shift work appears to take a heavy toll on some 
workers, while others appear unaffected or may even prefer 
it to "normal" work hours. For mining companies using 
shift work, it is important to recognize the potential nega- 
tive effects and select workers and a shift schedule to min- 
imize these negative aspects. Shift workers, for example, 
get about 25% less sleep than their day-working counter- 
parts (29). There appears to be little evidence, however, that 
life expectancy is reduced by shift work, or that sickness 
is increased among shift workers. 



In this chapter, an enormous amount of information and 
data have been presented concerning limitations and cap- 
abilities of humans as information receivers, processors, and 
action takers. Some of this information has direct relevance 
to mining, while much of it forms the basis for the design 
recommendations contained in subsequent chapters. 

The intent was not to provide an exhaustive discussion 
of human capabilities and limitation, but rather to illustrate 
the range of factors and abilities that affect human perfor- 
mance. This basic background information should aid in 
appreciating the following chapters on information displays, 
controls, tools, equipment design, physical work, etc. When 
people's capabilities are exceeded because of the task, equip- 
ment, and/or environment, errors increase, accident fre- 
quency increases, and productivity declines. People are not 
infinitely adaptable; they have limitations, and recognition 
of these limitations is a step toward designing for increased 
productivity and safety. 



REFERENCES 

1. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford. D.K. Caddel, 
K. Intaranont, S. Morrissey, and J.L. Salan. Mining in Low Coal. 
Volume II: Anthropometry (contract H0387022, Texas Tech Univ.). 
BuMines OFR 162(2)-83, 1982, 123 pp.; NTIS PB 83-258178. 

2. Bjerner, B., and A. Swensson. Shiftwork and Rhythm. Acta 
Med. Scand., Suppl. 278, 1953, pp. 102-107. 

3. Bobo, M., C. Burford, M. Ayoub, and K. Intaranont. Hazar- 
dous Occupations Showni Not To Increase Performance Times. Occu- 
pational Health and Safety, Mar. 1984, pp. 59-61. 

4. Bullock, M. The Determination of Functional Arm Reach Boun- 
daries for Operation of Manual Controls. Ergonomics, v. 17, 1974, 
pp. 375-388. 

5. Damon, A., H. Stoudt, and R. McFarland. The Human Body 
in Equipment Design. Harvard Univ. Press, 1966, 231 pp. 

6. Dempster, W. Space Requirements of the Seated Operator. U.S. 
Air Force Wright Air Develop. Center, Dayton, OH, TR-55-159. 
1955, 187 pp. 

7. Fitts, P. A Study of Location Discrimination Ability. Ch. in 
Psychological Research on Equipment Design, ed. by R. Fitts. Army 
Air Force Aviation Psychology Program, Dayton. OH. RR-19. 1947, 
pp. 87-113. 

8. Folkard, S., T. Monk, and M. Lobban. Short and Long Term 
Adjustment of Circadian Rhythms in "Permanent"' Night Nurses. 
Ergonomics, v. 21, 1978, pp. 785-799. 

9. Grandjean, E. Fitting the Task to the Man: An Ergonomic Ap- 
proach. Taylor and Francis, 1981, 379 pp. 

10. Hertzberg, H. Dynamic Anthropometry of Working Positions. 
Human Factors, v. 2, 1960, pp. 147-155. 

11. Hopkinson, N. Prevalence of Middle Ear Disorders in Coal 
Miners. NIOSH, Cincinnati, OH, DHHA-PN-81-101. 1981. 39 pp. 

12. Human Engineering Laboratory Detachment, U.S. Army 
Missile Command (Redstone Arsenal, ALl Human Engineering 
Design Data Dig., June 1978, 149 pp. 

13. Hunsicker, P. Arm Strength at Selected Degrees of Elbow 
Flexion. U.S. Air Force Wright Air Develop. Center. Davton. OH. 
TR 54-548, 1955, 87 pp. 

14. Huchingson, R. New Horizons for Human Factors in Design. 
McGraw-Hill, 1981, 512 pp. 

15. Johansson, G, and K. Runar. Drivers' Braking Reaction 
Times. Human Factors, v. 13, 1971, pp. 23-27. 

16. Kroemer, K. Human Strength: Terminology. Measurement, 
and Interpretation of Data. Human Factors, v. 12, 1970, pp. 297-313. 



33 



17. Martin, R., and R. Graveling. Background Illumination and 
Its Effects on Peripheral Visual Awareness for Miners Using 
Caplamps. Appl. Ergonomics, v. 14, 1983, pp. 139-141. 

18. McCormick, E., and M. Sanders. Human Factors in Engi- 
neering and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 

19. McDonald, B. Improved Truck Driver Alertness Technology 
(contract S3361341, Midwest Res. Inst.). BuMines OFR 84-77, 1977, 
25 pp., NTIS PB 266 852. 

20. Mead, P., and P. Sampson. Hand Steadiness During 
Unrestricted Linear Arm Movements. Human Factors, v. 14, 1972, 
pp. 45-50. 

21. Miller, G. The Magical Number Seven Plus or Minus Two: 
Some Limits on Our Capacity To Process Information. Psychological 
Rev., v. 63, 1956, pp. 81-97. 

22. Monk, T., and S. Folkard. Circadian Rhythms and Shiftwork. 
Ch. in Stress and Fatigue in Human Performance, ed. by R. Hockey. 
Wiley, 1983, pp. 87-115. 

23. National Academy of Sciences. Toward Safer Underground 
Coal Mines. 1982, 190 pp. 

24. President's Commission on Coal. Coal Data Book. GPO, 1980, 
83 pp. 

25. Sanders, M. Anthropometric Survey of Truck and Bus Drivers: 
Anthropometry, Control Reach and Control Force. Canyon Res. 
Group Inc., Westlake Village, CA, 1977, 63 pp. 



26. Sharp, E. Effects of Primary Task Performance on Response 
Time to Toggle Switches in a Workspace Configuration. U.S. Air 
Force Med. Res. Lab., Wright Patterson AFB, OH, AFAMRL- 
TR-190, 1967, 63 pp. 

27. Summala, H. Drivers' Steering Reaction to a Light Stimulus 
on a Dark Road. Ergonomics, v. 24, 1981, pp. 125-131. 

28. Tasto, D., and M. Colligan. Shift Work Practices in the United 
States. NIOSH, Cincinnati, OH, DHEW-PN-77-148, 1977, 62 pp.; 
NTIS PB 274 707. 

29. Tilley, A. The Sleep and Performance of Shift Workers. 
Human Factors, v. 24, 1982, pp. 629-641. 

30. U.S. Department of Defense. Human Engineering Design 
Criteria for Military Systems, Equipment and Facilities. MIL- 
STD-1472B, Dec. 31, 1974, 231 pp. 

31. Van Cott, H., and R. Kinkade. Human Engineering Guide 
to Equipment Design. Wiley, rev. ed., 1972, 752 pp. 

32. Wargo, M. Human Operator Response Speed, Frequency, and 
Flexibility: A Review and Analysis. Human Factors, v. 9, 1967, 
pp. 221-238. 

33. Wickens, C. Engineering Psychology and Human Perfor- 
mance. Charles E. Merrill, 1984, 544 pp. 



34 



CHAPTER 4.— HUMAN ERROR AND ACCIDENTS 





Accidents may happen but they can be avoided. 



On Monday, July 11, 1983, the 5 right section crew 
arrived at the working section. Because of absenteeism, 
most of the crew was composed of miners from the 18 left 
section. Richman, 1 a shuttle car operator, was in the No. 
2 entry with Nystrom, a maintenance worker. According 
to Nystrom, Richman was going to move the shuttle car but 
could not do so because the brake lock was set. Richman 
asked Nystrom where the lock was located and Nystrom 
pointed it out to him and released it. Richman also told 
Nystrom that he had never operated this particular model 
of shuttle car. The shuttle car he normally drove, although 
manufactured by the same company, was structurally dif- 
ferent. He trammed the shuttle car-to the section feeder to 
become familiar with its operation. 

After the test run, Richman moved the shuttle car 
behind the continuous miner and asked Upton, the contin- 
uous miner helper, to check his cable reel. Richman then 
angled his car beneath the continuous miner tail conveyor 
and loading began. Shortly thereafter, Richman got out of 
the operator's compartment, swiveled the seat to tram 
outby, and got back in. As he was looking toward the con- 
tinuous miner over his right shoulder, the car started to 
move; he said that he could not hold it. Richman saw Up- 
ton on the opposite side of the shuttle car, along the rib, 
and began yelling for him to get out of the way while try- 
ing to brake and hit the panic bar. The shuttle car pinned 
Upton against the rib and completely severed both his legs. 
Upton died shortly thereafter. 

What was the cause of this accident? Was it human 
error? Was it equipment failure? Was it a combination of 
both? Why was Upton standing where he was? Why couldn't 
Richman stop the shuttle car? 

As it turned out, the shuttle car showed no evidence of 
brake failure or any other malfunction. It was the consen- 
sus of the investigating team that when Richman became 
aware of the machine's movement toward Upton, he at- 
tempted to brake, but he engaged the tram rather than the 
brake pedal. Here then is a clear case of human error; or 
is it? The accident report also noted that the shuttle car's 
brake and tram control pedals were the exact opposite of 



those on the shuttle car Richman normally operated. Both 
cars were made by the same manufacturer but were dif- 
ferent models. Perhaps Richman made an error, but is he 
to blame for it? 

In this chapter the concepts of human error and acci- 
dent will be explored. Theories of accident causation will 
be discussed, and an analysis of mining accident statistics 
will be made. 



HUMAN ERROR 

Human error is often used as a synonym for operator 
error, although there are obviously other humans in the 
system besides the operator. The operator's immediate 
supervisor and the mine's manager are human, and they 
too can err. Improper work procedures, poor management 
policies, and inadequate supervision could all be causal fac- 
tors in an accident, and all are caused by humans. Main- 
tenance personnel are human, and their errors can be the 
cause of accidents. The designer of the equipment may also 
have erred, as perhaps was the case with Richman and Up- 
ton previously described. Thus, to think of human error only 
in terms of operator error is rather narrow and may be 
counterproductive with respect to accident investigation and 
prevention. 

When some people talk of human error, there is a con- 
notation of blame or cause, rather than considering human 
error as simply an event whose cause is yet to be deter- 
mined. One danger with the causal interpretation of human 
error is that the resultant emotional atmosphere often 
makes it difficult to rationally determine appropriate cor- 
rective action. 

In this chapter the term "human error" is considered 
to be an event that can occur anywhere in the system. The 
following definition is suggested by Conway and Sanders 
(7):* An inappropriate or undesired human decision or 
behavior that reduces, or has the potential to reduce, effec- 
tiveness, safety, or system performance. 



Names have been changed. 



1 Italic numbers in parentheses refer to items in the list of refcreiu 
the end of this chapter. 



35 



In addition to defining human error, numerous inves- 
tigators have attempted to develop classification systems 
to describe the nature of human errors. Some of these 
systems are simple, two-part classifications, while others 
are more elaborate and follow from the basic components 
of human information processing and performance. 

Broad Classification of Human Error 

One investigator (1 7) attempted to classify human errors 
into the following broad categories: operator-induced errors, 
design-induced errors, and system-induced errors. Operator- 
induced errors are incorrect conscious or unconscious ac- 
tions or decisions on the part of personnel who have the 
training, experience, and tools necessary to make correct 
decisions and actions. Design-induced errors are errors in- 
duced by poor equipment design, fabrication, installation, 
or operating procedures. System-induced errors result from 
such things as system integration, operational practices or 
procedures, management policies, and selection and train- 
ing procedures. 

An important point was made by Meister (17) with 
respect to this classification of errors. Many errors made 
by operators are not operator-induced errors, but could be 
design- or system-induced errors. The accident described at 
the beginning of this chapter is an example of just such a 
case. 

Action Classification of Human Error 

Action models focus on the output of the human in terms 
of decisions made and actions taken. The simplest classifica- 
tion is that suggested by Swain and Guttman (27): errors 
of omission, errors of comission, sequence errors, and tim- 
ing errors. 

Errors of omission involve failure to do something. The 
following is an example of an error of omission that resulted 
in a mining fatality (MSHA Fatalgrams, Jan. 2, 1981, 
81-09). 

An electrician was electrocuted while attempting 
to position himself on the steel framework of a substa- 
tion. There were several points to disconnect in order 
to shut off power completely to the substation. In this 
case something was missed. 

Errors of commission involve the incorrect performance 
of an act. The following is an example from MSHA 
Fatalgrams (Sept. 29, 1980, 80-039). 

The victim, sitting on the conveyor belt, called for 
his partner to hit the start button just lightly to jog 
the belt forward a few inches. The helper lost his 
balance momentarily, hit the button hard and actu- 
ally started the belt, rather than just jogging it for- 
ward. The victim was drawn between the belt and a 
steel support member 9 inches above the belt. 
A sequence error occurs when a person performs some 
task or step in a task out of sequence. A good example is 
the following (MSHA Fatalgrams, July 25, 1980, 80-033). 
A helper was killed when the crane he was oper- 
ating overturned. The victim lifted a 24 ton block with 
the boom extended 80 feet at a low angle. Instead of 
raising the boom first, the victim rotated the crane 
to the right 90 degrees, resulting in positioning the 
near-flat extended boom at right angles to the crawler 
tracks. This caused the crane to overturn. 
A timing error occurs when a person fails to perform 
an action within the allotted time, either too early or too 



late. An example would be a shot firer who does not vacate 
a blasting area fast enough after lighting fuses and is 
caught by the blast. 

Actually, both sequence and timing errors are errors of 
commission, but are listed separately because their causal 
factors are frequently different. As can be seen, this classi- 
fication focuses on operator errors as defined by Meister (1 7). 

Information-Processing Model of Human Error 

Several authors use an information-processing model 
to classify human errors. These models use an input, deci- 
sion, and output classification scheme. The output element 
overlaps the action classification discussed previously. One 
information-processing model is shown in table 4-1. A prob- 
lem with applying such a taxonomy is that often the same 
objective error can be classified into several categories, 
depending on the details of the situation. Such details are 
not often obvious from the description of the error or acci- 
dent. For example, a loading machine helper was scaling 
down broken roof. Two temporary supports had been set. 
A large piece of rock broke from the roof, drove out the two 
supports, and fell on the miner. How does one classify this 
based on table 4-1? Did the worker not detect the loose rock? 
Did he detect it, but not classify it as dangerous? Did he 
incorrectly estimate the protective capability of the sup- 
ports? As can be seen, such classification systems often re- 
quire more information than is available in an error 
situation. 

Table 4-1 .—Information-processing model of human error (8) 

Inputs Sensing. 

Detecting. 

Identifying. 

Coding. 

Classifying. 
Decisions Estimating. 

Logical manipulation. 

Problem solving. 
Outputs Chaining. 

Omissions. 

Insertions. 

Misordering. 

Copyright 1972 by McGraw-Hill Book Co., and reprinted by permission. 



Warning-Hazard Classification of Human Error 

Closely related to the information-processing model of 
human error is the classification scheme (15) used to 
investigate human errors in South African gold mining 
accidents. Table 4-2 presents the classification scheme 
and lists causes of the various types of human errors. 
This classification stressed the importance of perceiving 
and recognizing warnings about hazards in the work 
environment. 

Error classifications, such as those described, can serve 
several useful purposes: (1) facilitate the tabulation of er- 
ror frequencies, (2) provide a general frame of reference for 
studying human error, and (3) direct efforts at reducing the 
incidence of errors. The classifications that have been 
developed, however, are crude at best and have not served 
the needs of either the scientist or the practitioner. Fur- 
ther efforts at developing an error classification scheme 
could probably be better spent in identifying the causes of 
human error, and developing and validating preventive and 
remedial strategies. 



36 



Table 4.2— Human error classification of accidents in 
South African gold mines (15) 



Human error 
Failure to perceive a warning 



Failure to recognize a 
perceived warning. 



Underestimation of hazard . 
Failure to respond to a 

recognized warning. 
Responded to warning but 

ineffectively. 



Inappropriate secondary warning 



Cause 
Inadequate inspection technique. 
Neglecting to inspect. 
Obstruction to line of sight. 
Masking noise. 
Other. 

Mixture of these. 
Inadequate information. 
Lack of training. 
Lack of experience. 
Other. 

Mixture of these. 
Causes unknown. 
Underestimation of hazard. 
Other. 

Negligence or carelessness. 
Standard practice inappropriate. 
Well-intended but ineffective direct 
action. 
Other. 

Mixture of these. 
Causes unknown. 



Copyright 1974 by National Council, and reprinted by permission. 



WHAT IS AN ACCIDENT 

Before anything can be scientifically studied, it must 
be defined. Although this may sound easy with respect to 
accidents, in fact, definition has been a stumbling block to 
accident research since its inception. Consider the follow- 
ing example. A haulage truck operator fails to visually in- 
spect the area in front of his or her truck before starting 
out. In one case, the operator drives off and nothing hap- 
pens. In another case, the operator runs over a person stand- 
ing in front of the truck; and in yet another case, he or she 
crushes a small vehicle as shown in figure 4-1, but no one 
is hurt. Is the first case an accident? One might consider 
it an error; but when does an error become an accident? 
Must there be injury or property damage in order for an 
accident to be considered an accident? 

In defining the term "accident" it is necessary to dis- 
tinguish between the act itself and the consequence of that 
act. Two extreme definitions can be identified, but there 
are many shades and blends of definitions between them. 
For example, 200 different definitions of accidents were col- 
lected by Benner (2). At one extreme, definitions take no 
account of the consequences of the act, but rather define 
an accident in terms of the characteristics of the act itself. 
For example, a list of accident indicators was produced by 
Suchman (26); the more indicators that were present, the 
more the event was likely to be called an accident. The in- 
dicators were 

1. Low degree of expectedness. 

2. Low degree of avoidability. 

3. Low degree of intention. 

At the other extreme are definitions that stress the con- 
sequence of the act. For example, acts that result in injuries 
are considered to be accidents. For the most part, the min- 
ing industry has adopted the consequence-type definition, 
and for all practical purposes defines accidents as synony- 
mous with injuries. 



If consequence is considered the principal element in 
the definition of an accident, then the following conse- 
quences must be distinguished: 

1. Fatal injury. 

2. Nonfatal injury that results in days lost from work. 

3. Nonfatal injury that results in restricted work days. 

4. Nonfatal, no-days-lost injuries (also called first-aid 
injuries). 

5. Property damage. 

One might think that such categories would be clear 
and unambiguous. However, when 14 mine safety person- 
nel were asked to classify four injury cases as disabling, 
nondisabling, or neither, the results indicated disagreement 
with respect to whether an injury was disabling or non- 
disabling (20). 

One common belief is that chance or luck distinguishes 
a fatal accident from a nonfatal accident. A little reflection, 
however, reveals that some activities are more likely to 
cause one type of consequence than another. For example, 
a study of coal mine accidents in Great Britain over a 3-yr 
period (19) found that, as would be expected, a greater pro- 
portion of fatalities occurred in haulage and transport than 
in handling materials and using handtools. The results were 
just the opposite for nonfatal injuries. 

Serious accidents (all those that resulted in at least 1 
day of restricted or missed work activity) in underground 
and surface mines from 1975 to 1982 were investigated by 
Bennett and Passmore (3). The probability that an injury 
would be severe increased in each succeeding year studied; 
was lower for supervisory and maintenance personnel than 
for all other job classifications; and was not any greater for 
younger or more inexperienced miners than for older or 
more experienced miners. 

Several investigators have urged the use of near-miss 
accidents as a source of information on accident causation. 
The logic behind this is that there are more near-miss ac- 
cidents than injury-producing accidents, and therefore more 
data are available for study. It is assumed that only chance 
and luck discriminate a near-miss accident from an actual 
accident. An investigation of near-miss accidents in British 
coal mines (23) was made by asking miners once per month 
to describe any near-misses they experienced. Two problems 
with this approach are (1) there may be selective recall, e.g., 
the miners may tend to recall near-misses that they felt 
responsible for and may tend to forget those that were 
caused by forces over which they had no control; and (2) the 
definition of a near-miss is vague, i.e., how near a miss does 
it have to be to call it a near-miss. These types of problems 
make it difficult to use near-miss data to estimate the 
relative contribution of various causal factors because only 
a sample of all near-misses are reported, and this sample 
is very likely unrepresentative of the population of near- 
misses actually occurring. 



HUMAN ERROR AND ACCIDENTS 

What percentage of accidents is caused by human er- 
ror? This is a question that has vexed researchers for years. 
Probably the most common answer one hears is that ap- 
proximately 85% of accidents are due to human error. This 



37 




Figure 4-1 .—One consequence of operator error. 



figure came from an analysis of insurance company records 
conducted by Heinrich (11). This percentage, however, 
should not be taken too seriously. The percentage of acci- 
dents one attributes to human error depends on how one 
defines human error; the data source used to compile the 
statistics; and the alternative causes, other than human er- 
ror, included in the tabulation. 

If one assumes that human beings are responsible for 
their own actions and are therefore responsible for the er- 
rors they make, then a higher percentage of accidents will 
be attributed to operator error. On the other hand, if the 
view is adopted that errors can be anticipated and they 
should therefore be planned for and designed for, and that 
when they do occur the fault should be traced to the 
designer, then fewer accidents will be attributed to operator 
error. 

The typicial human-error-in-accident investigation clas- 
sifies cause as either due to unsafe acts (i.e., operator error) 
or unsafe conditions, or as due to operator error or equip- 
ment failure. Such a simple classification results in a 
foregone conclusion that a high percentage of accidents will 
be attributed to the operator. Such analyses leave out the 
all important question of what caused the operator to err. 
Often the cause can be traced to faulty equipment design, 
inadequate or improper instruction and training, or dan- 
gerous management policies. 



A review of the literature reveals widely disparate esti- 
mates of the percentage of accidents due to human error. 
For example, in 12 studies reviewed by Conway, Muckler, 
and Peay (6), percentages were found ranging from 4.3% 
to 90%. Half reported percentages equal to or exceeding 
80%, while the other half reported percentages less than 
or equal to 50% 

A few studies have attempted to estimate the propor- 
tion of accidents in the mining industry attributable to 
human error. A study of underground transport accidents 
in Great Britain (10) revealed that 44% of the accidents were 
due to "lack of discipline or ordinary caution" and "bad 
operator practice." Sims, Graves, and Simpson (23) categor- 
ized haulage near-misses as caused by "man factors" (i.e., 
human errors), "vehicle/load factors," or "environmental 
factors." They reported that 49% of the incidents were 
caused by "man factors." On the other hand, it was reported 
by Snyder (24) that, based on Mine Safety and Health 
Administration accident investigations, 63% of the 43 fatal 
accidents involving supervisors from 1981 through July 
1983 involved the victims doing things they knew, or should 
have known, were unsafe. These acts included the victims 
placing themselves in a hazardous position; standing or 
working in areas where the roof was not supported or where 
an approved roof control plan was not being followed; repair- 
ing machinery in motion or electrical equipment that was 



38 



known to be energized; supervising improperly conducted 
blasting operations; or overseeing work in operations with 
inadequate ventilation. 

From an analysis of 92 underground mining accident 
investigations, it was found by Sanders and Shaw (21) that 
operator error was involved to some degree in 93% of the 
cases, but was the primary cause of only 39% of them. 
Across all 92 cases, the average percentage of cause attrib- 
uted to operator error was 30.5%. 

Lawrence (25), in his investigation of 405 South African 
gold mining accidents, identified 794 errors associated with 
the perception of, recognition of, and response to warnings. 
His investigative model assumed that all accidents were 
due to human errors, and his task was to categorize the er- 
rors by type. These error classifications and causes are 
shown in table 4-2. A careful reading of the causes listed 
for a human error indicate that some of them would be con- 
sidered, according to Meister (17), as design errors (e.g., 
obstruction to the line of sight or masking noise), or system 
errors (e.g., lack of training or inappropriate standard prac- 
tice). The percentages of accidents assigned to his classifica- 
tion of errors by Lawrence (15) were as follows: 

Failure to perceive a warning 36% 

Failure to recognize a perceived warning 4% 

Underestimation of hazard 25% 

Failure to respond to a recognized warning . . . 17% 

Responded to warning but ineffectively 14% 

Inappropriate secondary warning 4% 

It appears that there is probably no one answer to the 
question of the contribution of human error to accidents. 
The best that can be said is that the answer depends on what 
human error is considered to be, and whether the cause of 
the error is taken into account. Overall, however, it can 
probably be said that operator error is the primary cause 
in no more than half of the accidents occurring in 
underground mining. This conclusion is based on the results 
of the studies by the Health and Safety Executive (10), 
Sanders and Shaw (21), and Sims, Graves, and Simpson (23). 



THEORIES OF ACCIDENT CAUSATION 

There has been a wide array of accident causation 
theories proposed. Each theory emphasizes the orientation 
of its author, be it psychological, sociological, or statistical. 
The varying theories can, however, be grouped into three 
broad classes: accident proneness theories, job demand ver- 
sus worker capability theories, and psychosocial theories. 

Accident Proneness Theories 

The oldest and probably the most influential accident 
causation theory is that of accident proneness. In its pure 
form it hypothesizes that some people are more prone to 
have accidents than others because of a peculiar set of 
constitutional characteristics. Further, accident proneness 
is considered to be a relatively permanent feature of the 
individual. 

The support for this theory has come from statistical 
comparisons between the distribution of accidents in a 
population of workers and the distribution expected by pure 
chance. What was often found was that more people than 
would be expected had multiple accidents. More recent 
authors have challenged these early statistical studies, 
pointing out that to accept accident proneness one must 
accept the underlying assumption that all people in a pop- 



ulation of workers are exposed to the same job and envi- 
ronmental hazards. The fact that more people have multi- 
ple accidents than would be expected because of chance may 
only indicate that some people are exposed to more hazards 
on the job than others. 

A more restricted view of accident proneness is that peo- 
ple are more or less prone to accidents in given specific situa- 
tions, and that this proneness is not permanent but changes 
over time. This has been called the accident liability theory. 
Thus, person A may be more accident prone than person 
B in situation 1; but in situation 2, person B may be more 
accident prone than person A. Further, person A may be 
more accident prone than person B in situation 1, but this 
proneness may decrease with time. 

Two prime variables that relate to this formulation of 
accident liability are age and experience. The problem, 
however, is that it is often difficult to separate the effects 
of the two variables; younger workers usually are also the 
most inexperienced. Little relationship was found among 
underground coal miners between age and either fatality 
rates or permanent disabling injury rates (18). There was, 
however, a very strong correlation between age and nonper- 
manent disabling injury rates. Figure 4-2 depicts the rela- 
tionship found. A young miner (18-24 yr old) was about three 
times more likely to be injured than a miner 45 yr of age 
or older, and about twice as likely to be injured than a miner 
25 to 44 yr of age. 

A number of researchers have suggested that younger 
workers have accidents for reasons other than experience. 
For example, inattention, lack of discipline, impulsiveness, 
recklessness, misjudgment, overestimation of capacity, and 



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o 

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o 
o 
o 
o* 

o 

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25 



20 - 



15 - 



10 



5 - 

















- 






- 








- 


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18-24 25-34 35 "44 
AGE GROUP, yr 



>45 



Figure 4-2.— Relationship between age and disabling injury 

rate (23). (Courtesy of National Academy Press) 



39 



pride were implicated by Lampert (14) as factors that may 
account for higher accident rates among younger workers. 

Although not investigated by the National Academy of 
Sciences (18), other investigators have found that accident 
liability increases among older workers (e.g., over 50 or 60 
yr of age). This increase may be due to deterioration in 
motor skills, sensory functions, and mental agility (9). It 
should be pointed out that Schaffer, Gavan, and Woodward 
(22) found no such rise in accident liability at the upper age 
range for operators of surface front-end loaders, haulers, or 
trucks, nor for operators of underground shuttle cars or roof 
bolting machines. 

The amount of job experience is another transient fac- 
tor that changes an individual's accident liability over time. 
Virtually all investigators have found experience to be 
closely related to accident liability. Further, it appears that 
specific job experience is more important than general min- 
ing experience. The number of days of experience at a new 
job element (new mine, new job, new piece of equipment, 
new task, etc.) were found to be related to fatal accidents 
(28). The accident frequency on the first day was nearly 
three times higher than the average frequency for the next 
4 days. This conclusion was supported by Studenski (25) 
when he found that 40% of mistakes that resulted in ac- 
cidents at work occurred on rarely performed or entirely 
new tasks. 

Even among supervisors, experience is an important fac- 
tor in accidents. Among coal mine supervisors who were 
killed in the 9-yr period from 1973 through 1981, 31% had 
2 yr or less of supervisory experience. Figure 4-3 shows a 
more detailed analysis of 49 supervisors who died in coal 
mine accidents from 1981 through July 1983. As can be 



10 




uuv\n , u , Q_ 



UJ 

H 

13 5 
< 



10 




£ 



U\A, 171, F1M 



H 



V\ 



J2L 



Hffl 



^A\ArXA 





J 



/ 



PHM , U\7\ 



-2 



6 8 10 12 14 
EXPERIENCE, yr 



16 



18 20 22 



Figure 4-3.— Supervisor fatalities in coal mining as a function 
of experience at mine (A), experience in job classification (8), 

and total mining experience (C) (24). (Courtesy of U.S. Mine Safety and 
Health Administration) 



seen, experience in job classification and experience at mine 
are highly related to accident frequency, while the relation- 
ship of total mining experience to accident frequency is less 
discernible. It indeed appears that accident liability fluc- 
tuates with time, especially as related to age and specific 
job experience. The notion that some people are naturally 
more accident prone than others across all situations and 
at all times is probably a less tenable position. 

Job Demand Versus Worker Capability Theories 

This class of theories is related in part to the accident 
liability notion previously introduced. Simply put, accident 
liability increases when job demands exceed worker capa- 
bilities. For example, if a job requires greater psychomotor 
skills than workers have, accidents are expected to increase. 
The relationship between job experience and accident rates 
can also be considered as examples of job demands exceeding 
worker capabilities. With more experience, capabilities in- 
crease and, hence, one would expect accidents to decrease. 

Another line of evidence used to support this class of 
theories is the relationship of fatigue to accidents. The 
assumption is that with increased fatigue, capabilities are 
reduced. Because it is difficult to measure fatigue, in- 
vestigators have correlated accident frequencies with fac- 
tors believed to be related to fatigue, such as day of week, 
time of day, and time since shift started. 

The problems with studies that have investigated day 
of week, time of day, etc., are that they do not attempt to 
equate the number of people actually working on each day 
of the week, the hour of the day, etc.; and they do not at- 
tempt to equate the type of work being performed on each 
day of the week, the hour of the day, etc. For example, it 
was noted by Adams, Barlow, and Hiddlestone (1) that fewer 
accidents occur on Mondays and a greater number of ac- 
cidents on Wednesdays. It may well be that absenteeism 
is higher on Mondays than in the middle of the week. They 
also reported a steady increase in the number of accidents 
occurring 40 to 70 min after a break, with a consistent and 
steady drop thereafter. One factor affecting this steady drop 
after 70 min may be that another break may be in progress 
because there are not many workers who fail to take a break 
of some sort after 90 min of work. 

Unfortunately, then, this line of research cannot be used 
to support the job demand versus worker capability theories. 
Some tangential evidence, however, came from a study by 
Kephart and Tiffin (12) who investigated the visual require- 
ments of 12 jobs and compared them to the workers' visual 
capabilities. In 11 of the 12 jobs, the percentage of safe 
workers (low-accident employees) was higher among those 
whose capabilities exceeded the requirements than among 
those whose capabilities did not exceed the requirements. 

Related to the job demand-worker capability class of 
theories is the adjustment to stress theory. This theory 
states that accident rates will be higher in situations where 
stress (physical or physiological-psychological) is placed on 
the worker. In essence, the additional stress overloads the 
workers and adds to the demands of the job so that their 
capabilities no longer match the job demands. Physical 
stressors include noise, poor illumination, and temperature 
extremes. Physiological-psychological stressors could in- 
clude anxiety, lack of sleep, illness, anger or remorse from 
having a fight with a spouse, etc. The research data are 
mixed with respect to the effects of these variables. Un- 
doubtedly, some of the confusion arises because the jobs per- 
formed, even with the stressors, are not demanding enough 



40 



to exceed the worker' capabilities; or the workers slow down 
and this reduces the overall demands of the job. 

Psychosocial Theories 

One theory, goals-freedom-alertness, holds that greater 
freedom among workers to set reasonably attainable goals 
is accompanied by high-quality work performance, and ac- 
cidents are viewed as examples of low-quality work perfor- 
mance. The idea is that by raising the level of alertness, 
accidents will be reduced; and this alertness can be sus- 
tained only within a rewarding psychological climate (13). 
Kerr contends that in industry, both management and 
unions interfere with this climate by telling people what 
to do and what not to do, without asking them their ideas 
about relevant and attainable goals. Sanders, Patterson, 
and Peay (20) found some evidence supporting this theory 
among underground coal miners. This study will be dis- 
cussed further in chapter 10. 

In addition to the goals' freedom-alertness theory, there 
are some psychoanalytical theories that view accidents as 
self-punitive acts caused by guilt, aggression, etc. 

Overall, then, there does not appear to be any one really 
good theory of accident causation. All have a ring of truth 
to them, but by themselves do not explain the complexity 
of the accident situation. 



INJURY STATISTICS 

Numbers seem to be so objective; it is possible to com- 
pute the number of trip-and-fall injuries, compare them to 
back injuries, look for trends over several years, and make 
recommendations based on the "statistics." For some 
unknown reason, putting a number on something makes 
it more believable. Nothing is inherently wrong with this, 
as long as the limitations of the numbers used are under- 
stood. Consideration must be given to how the data were 
collected, and what factors could have influenced the 
numbers obtained. 

Mining companies may collect, tabulate, and analyze 
their own accident data. The Mine Safety and Health Ad- 
ministration (MSHA) of the Department of Labor requires 
mining companies to report accidents and fill out accident 
forms so that MSHA can collect, tabulate, and analyze the 
resulting data. The entire accident-reporting process, from 
accident occurrence to reporting, is at best an unreliable 
process that almost always fails to capture all the accidents 
that actually occur. In addition, the data collected about 
the accidents are often inaccurate and incomplete. 

As already discussed in this chapter, the term "acci- 
dent" has many definitions, and the definition accepted will 
obviously influence the type and the number of incidences 
reported. Even if accident and injury are accepted as syn- 
onymous terms, there is still plenty of opportunity to lose 
data. 

Sanders, Patterson, and Peay (20) traced the injury- 
reporting process to the last step, transmitting the data to 
MSHA, and revealed several areas where injury data may 
be lost. 

Workers commit unsafe acts, a proportion of which lead 
to injuries. Workers must then decide to report the injuries 
to management. In cases of serious injuries, there is little 
choice. With less serious injuries (e.g., cut or bruised fingers, 
strained back, or dust in the eye), however, workers may 
decide not to report injuries for any number of reasons (e.g., 



they know management does not like workers who belly- 
ache, they are afraid they may be laid off, their pride keeps 
them from admitting to injuries, they feel they can treat 
the injuries themselves, etc.). 

After a worker reports an injury, management decides 
if it is really an injury. Again, with minor injuries, manage- 
ment may question whether an injury really occurred (e.g., 
back strain) or may say, "Put a bandage on it and forget 
it." If an injury is considered bona fide, management then 
decides whether it is a lost-time injury. Surprisingly, there 
is some ambiguity here. A worker can be told to go home 
and take a few days off to recuperate, creating a lost-time 
injury; or the worker can be given a temporary assignment 
in the office or topside where recuperation can take place 
while the employee is on the payroll, without a lost-time 
injury. This practice often exists in industry. 

At each of the steps in this process, an injury may drop 
out and not be reported. Some companies may report more 
injuries than do others because of differences in reporting 
policies rather than in the underlying safety of the mines. 
If injury statistics are used in a punitive fashion, then com- 
panies are more likely to underreport incidences. 

The accident data collected on an injury can also be a 
problem area. There is considerable confusion as to how an 
accident should be classified. Especially ambiguous is the 
source of injury category that identifies the object, sub- 
stance, exposure, or bodily motion that directly produced 
or inflicted an injury. Often, the nature of injury can be am- 
biguous, especially in the case of multiple injuries. The 
specification of accident type becomes difficult when the ac- 
cident sequence comprises a series of associated events. One 
worker drops a wrench. The wrench strikes another worker 
who is standing on a ladder. This worker falls off the lad- 
der, and the ladder in turn falls on him or her. Should this 
accident be classified as struck by falling object, and if so, 
by wrench or ladder, or as fall from ladder? 

The data collected usually concentrate on the individual 
injured, recording his or her age, experience, activity at time 
of injury, job title, etc. This is done whether or not the vic- 
tim was the cause of the accident or simply the recipient 
of another person's error. For example, if a continuous 
miner operator (50 yr old with 15 yr of job experience) 
crushes his or her helper (21 yr old with 1 yr of job experi- 
ence) against the rib with the tail conveyor of the continuous 
miner, the victim's injury is attributed to youth and inex- 
perience, when it may well be the fault of the older, more 
experienced operator. 

With these limitations in mind, a review is made of some 
of the following basic injury statistics in the mining 
industry. 



Industry-wide Comparisons 

The major sectors of the mining industry can be grossly 
categorized within a two-dimensional matrix: commodity 
by type of mine. Although these dimensions can become 
complex, as far as injury statistics are concerned, the situa- 
tion is simplified by dividing commodity into coal, metal, 
and nonmetal categories, and type of mine into underground 
and surface. This rough classification scheme is used by 
MSHA to tabulate its injury statistics. MSHA does, how- 
ever, include finer breakdowns within each of these 
categories. 

Figure 4-4 presents injury data for 1983 (29) for the 
various segments of the mining industry. Shown are the 



41 



percentages of fatal, nonfatal-days-lost (NFDL), and no-days- 
lost (NDL) injuries occurring in each industry segment. As 
can be seen, underground coal mining accounted for approx- 
imately 65% of all fatal injuries, 70% of all NFDL injuries, 
and 50% of all NDL injuries occurring in the mining in- 
dustry during 1983. These values are typical; similar values 
canbefound in other years as well. It is not surprising then 
that much more research effort has been directed toward 
understanding the causes of injuries in underground coal 
mining than in any other segment of the industry. 

Figure 4-5 shows the injury rates (per 200,000 employee- 
hours) for each segment of the industry for 1983 (29). As 
can be seen, the main distinction is between underground 
and surface mines, with smaller differences among com- 
modities. This is reinforced in figure 4-6, which shows the 
percentage of NFDL injuries attributed to the five main 
accident-producing categories for each segment of the in- 
dustry (metal and nonmetal have been combined). These 
five categories (handling materials, machinery, powered 
haulage, slips and falls, and handtools) accounted for the 
following percentages of NFDL injuries in 1983: 

Underground coal 83% 

Underground metal-nonmetal 79% 

Surface coal 93% 

Surface metal-nonmetal 91% 

For some categories, there is no apparent relationship 
among the segments of the industry, such as for handtool, 
powered haulage, and materials handling accidents. A 
greater proportion of accidents involved machinery in 
underground mining than in surface mining, probably due 
in part to the proximity of people to machinery, often in 
cramped work areas. A greater percentage of NFDL ac- 
cidents were slips and falls in surface mines than in 
underground mines. This is due in part to slips and falls 
while mounting and dismounting large surface mining 
equipment. The large percentage of "other" accidents in 
underground mining was due to roof fall injuries. The 
analogous situation in surface mining would be an injury 
due to failure of a highwall, to which fewer people are 
exposed. 



80 



60 



40 



o 
H 20 




KEY 

I I Fatal injury 

E3 Nonfatal-days-lost injury 

H No-days-lost injury 



si 



rJ 1T-M 



Coal Coal Metal Metal Nonmetal Nonmetal 

underground surface underground surface underground surface 

SEGMENT OF INDUSTRY 

Figure 4-4.— Percent of fatalities, nonfatal-days-lost, and no- 
days-lost injuries occurring in 1983 for each of the major 

Segments Of the mining industry (29). (Courtesy of U.S. Mine Safety and 
Health Administration) 




uj 5 
Q. 



KEY 
Nonfatal-days-lost injury 
No-days-lost injury 



_ B 




Coal 



Metal 



Nonmetal 



SEGMENT OF INDUSTRY 

Figure 4-5.— Nonfatal-days-lost and no-days-lost injury rates 
for 1983 for each of the major segments of the underground (A) 

and Surface (B) mining industry (29). (Courtesy of US Mine Safety and 
Health Administration) 



40 



CO 
UJ 

or 



v> 20 

Q 






< 

£ 40 
u. 

z 
o 

z 



S 20 

< 



UJ 

o 
or 

UJ 

o. 



A 


| 




KEY 
EZlCoal 
■■ Metah nonmetal 





















B 























$ 






^ 



^ 






<v 



*< 



*> 



SOURCE OF INJURY 



Figure 4-6.— Comparison of nonfatal-days-lost injuries from 
major accident catagories for the major segments of the under- 
ground (A) and surface (0) mining industry in 1983 (29). (Courtesy 

of U.S. Mine Safety and Health Administration) 



42 



it appears that much of the variance in injury statistics 
is due to the type of mine (underground or surface), and that 
underground mining is more hazardous than surface min- 
ing. Further, underground coal mines account for the ma- 
jority of mining industry injuries. For this reason, statistics 
from underground coal mining will be concentrated on and 
data from other segments of the industry will be addressed 
only where appropriate. 

Underground coal mines have been traditionally viewed 
as having high fatality rates. Compared with fatality rates 
of other industries, this is true. Compared with other types 
of underground mining, it may not be so. In 1983, for ex- 
ample, the fatality rate was higher in both metal and non- 
metal underground mining than in underground coal min- 
ing. Figure 4-7 shows the fatality rate for underground coal 
mining from 1932 to 1983 (18, 29-32). As can be seen, the 
general trend has been one of declining fatality rates over 
the recent past. 



Comparisons With European Countries 

It is difficult to make meaningful comparisons of U.S. 
injury rates with those of European countries. For one thing, 
mining conditions and methods are different. U.S. mines 
are generally less deep than European mines; room-and- 
pillar method is predominant in the United States, while 
longwall is predominant in Europe; labor is distributed dif- 
ferently in European mines than in U.S. mines; and the 
social systems and market conditions are different. Another 
problem is that reporting differences exist among countries. 
A disabling injury in the United States, is an injury that 
results in 1 day of missed work. In some European coun- 
tries, an injury is not classified as disabling until 3 days 
of work are missed. 

The number of fatalities is the only measure, therefore, 
that is directly comparable among countries. Even compar- 
ing the number of fatalities, however, can be tricky because 
of the need to take exposure into account. Comparing the 
number of fatalities per 1,000 workers among countries 
assumes that there are the same number of hours per shift 
in different countries, which is not true (16). If one compares 
U.S. underground coal mine fatalities per 100 million labor 
hours with those of European countries, one finds that the 
United States has a poorer record. This is shown in figure 
4-8A. It should be mentioned that the fatality rate in the 
United States has been dropping more rapidly than in Euro- 
pean countries, and is now approaching the European levels. 

What these statistics fail to present is the fact that U.S. 
mines are more productive than European mines. Therefore, 
when fatalities are computed per 100 million st of coal 
mined, the picture is radically different, as shown in figure 
4-8S. Here, the U.S. record is better than that of most Euro- 
pean countries, but more rapid improvements in productiv- 
ity are occurring in European mines, so that the differences 
are becoming smaller. 



COST OF ACCIDENTS 

Determining the cost of accidents can be a complex and 
unending process. The problem is determining which cost 
factors to include in the calculations. One end of the spec- 
trum could consider only the immediate medical compen- 
sation costs associated with various types of injuries. For 
example, medical expenses connected with underground 



0.4 



Federal Cool Mine Health and 
Safety Act of 1969 




1930 



1940 



1950 



I960 
YEAR 



1970 



I960 



1990 



Figure 4-7.— Fatality rate per 200,000 employee-hours for U.S. 
underground coal mines from 1931 through 1983 (18, 30-32). 

(Courtesy of National Academy Press and U.S. Mine Safety and Hearth Administration) 



Ul X 
Q_ Ld 

UJ 

UJ >- 

n 

£ i 

o 
o 



1 50 



IOO - 




300 



i° 

<r 

UJ 
Q. 



200- 



IO0- 



KEY 
C^ United Kingdom 
m Germany 
HE] France 
&&J European Common Market 




1950-64 



1965-69 1970-74 1975-77 

PERIOD 



Figure 4-8.— Comparison of fatality data between U.S. and 

European underground COal mines (18). (Courtesy of National Academy 
Press) 



coal mine injuries over an 18-month period for one large 
company were reported by Cain and Pettry (4\ Table 4-3 
shows the dollar amounts paid for various types of injuries. 
The 558 incidents cost this mining company approximately 
$217,950 or an average of $390.58 per incident in medical 
expenditures alone. 

Anyone who thinks such figures represent the total cost 
of injuries is naive. The most comprehensive analysis of ac- 
cident costs was carried out by FMC Corporation under a 
Bureau contract. A review of that effort was given by Phi 



43 



Table 4.3—1982-83 medical compensation costs paid 

per incident by a major coal company, by type 

of injury sustained (4) 



900 



Incidents 



15 

154 

35 

15 

26 
4 
29 
46 
10 
32 
168 
24 



558 



Cost 



Incident 



$178.25 

219.47 

90.89 

61.22 

2,601.17 

3,416.37 

36.59 

135.95 

80.84 

299.25 

406.18 

422.48 



390.58 



Type 1 



$2,675 

33,800 

3,180 

920 

67,630 

13,665 

1,060 

6,255 

810 

9.575 

68,240 

10,140 



217,950 



Abrasion 

Bruise 

Bruise and cut 

Burn (minor) 

Fracture: 

Simple 

Compound 

Irritation-inflammation 

Laceration 

Puncture 

Sprain 

Strain 

Other 

Total or average . . . 

1 Rounded. 



and DiCanio (5). The study and resulting predictive model 
considered the following cost factors: 

1. Loss of personal income. 

2. Compensation of wages from State, Federal, and union 
funds for disabling injuries. 

3. Benefits for injuries resulting in death or permanent 
disablity. 

4. Medical treatment and hospital care. 

5. Immediate and postaccident production losses as a 
result of a fatality or amputation injury. 

6. The costs incurred by the investigation of a fatal 
accident. 

The cost elements excluded were loss of life, fines, costs 
of lawsuits, loss of equipment, production loss due to a per- 
manent shutdown, immediate loss of production due to the 
disruptive effect of an injury serious enough to require 
medical attention, potential postaccident loss of production 
due to temporary replacement of an injured miner by a less 
experienced one, and cost of long-term followup treatment. 
The reason for these exclusions was simply that such costs 
are not readily available for analysis. Thus, the FMC model 
must be considered conservative at best. 

Figure 4-9 presents the findings on the average cost of 
a fatality for the various segments of the mining industry, 
and figure 4-10 presents the average cost of a disabling in- 
jury. As can be seen, the average cost of injuries has been 
increasing faster than the inflation rate for the last several 
years. The average industry cost in 1981 for a fatality was 
$674,000 and the cost of a disabling injury was $177,000. 

A significant portion of the costs incurred was due to 
postaccident declines in production. In the case of fatalities, 
all underground cases lost production from mine and sec- 
tion closures immediately following the accident. Further, 
in 73% of the cases, postaccident production level was sig- 
nificantly lower than preaccident production level for up 
to 5 months after normal operations resumed. Figure 4-11 
shows a typical example of the effect of an accident on pro- 
ductivity. In the majority of cases, the largest decline in 
productivity was not in the section that had the accident. 
After underground fatalities, for example, production 
declines in a majority of the sections. This demonstrates 
that a fatal accident affects all crews in a mine. 

The immediate and long-term production loss for cases 
involving fatal accidents in underground coal mining 
ranged from 0.5% to 9.4% of annual mine production, with 
a mean of 2.7%. At a price of $25.00 per short ton of coal, 




300 



1975 



1977 



1979 



1981 



YEAR 



Figure 4-9.— Average cost of a fatality in the mining industry 

1975-81 (5). (Courtesy of American Mining Congress) 



250 



— ' 1 ' 1 ' 

KEY 
o Underground coal 
d Surface coal 
200 |— A Underground metal-nonmetal 
O Surface metal-nonmetal 



</> 



.2 I50 - 



o 
•a 

ro 

O 



if) 
O 
O 



— Average 





1 975 



1 



1 



977 1 979 

YEAR 



1981 



Figure 4-10.— Average cost of a disabling injury in the mining 

industry, 1975-81 (5). (Courtesy of American Mining Congress) 



44 



200 



,-g I60h 



O S 

I- -5 

o > 

o 

o c 

Or 33 



120- 



80 



40' — 
-150 




-50 

WORK DAYS 



100 



Figure 4-1 1 .—Example of characteristic effect of a fatal injury 
on production in an underground mine, where the vertical axis 
represents production over preaccident levels and the preacci- 

dent level equals 100 (5). (Courtesy of American Mining Congress) 



the average mine lost $450,000 in production value from 
a fatality. One case resulted in a loss of $2,000,000. 

For fatal cases in underground metal mines, the pro- 
duction loss ranged from 0.5% to 4.0% of annual produc- 
tion, with a mean of 1.8%. There was no significant post- 
accident loss observed after fatalities in surface mines. 



DISCUSSION 

This chapter stressed the complexity of accidents and 
the role of human error in accidents. A total systems per- 
spective was stressed in which human error itself could be 
caused by inadequate equipment designs, management 
policy, and the like. The need to dig deeper to uncover these 
root causes was emphasized. A review of the major classes 
of accident causation theories revealed no one really good 
theory that accounts for all the data. Although accidents 
appear to be decreasing in the mining industry, there will 
continue to be a level of accidents and injuries considered 
by many to be unacceptable. Unfortunately, there is still 
much not known about the causes of mining accidents, and 
there remains more questions than answers in the field. 



REFERENCES 

1. Adams, N., A. Barlow, and J. Hiddlestone. Obtaining Ergonom- 
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2. Benner, L. Accident Investigations— A Case for New Percep- 
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3. Bennett, J., and D. Passmore. Probability of Death, Disabil- 
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4. Cain, R., and R. Pettry. Investigation of Medical Costs Cor- 
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11. Heinrich, H. Industrial Accident Prevention. McGraw-Hill, 
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12. Kephart, N., and J. Tiffin. Vision and Accident Experience. 
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13. Kerr, W. Complementing Theories of Safety Psychology. J. 
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14. Lampert, U. Age and the Predisposition to Accidents. Archives 
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15. Lawrence, A. Human Error as a Cause of Accidents in Gold 
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16. Marovelli, R. A Comparison of American Safety Performance 
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17. Meister, D. Human Factors: Theory and Practice. Wiley 
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18. National Academy of Sciences. Toward Safer Underground 
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19. Nussey, C. Studies of Accidents Leading to Minor Injuries 
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20. Sanders, M.S., T.V. Patterson, and J.M. Peay. The Effect of 
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Investigations in the British Coal Mining Industry. Paper in Pro- 
ceedings of the 1984 International Conference on Occupational 
Ergonomics, Toronto, Canada, May 7-9. 1984, pp. 203-215. 

24. Snyder, K. Supervisors' Deaths Often Linked to Earlier Dis- 
ruption of Routine. Mine Safety and Health, Winter-Spring. 1984, 
pp. 2-13. 

25. Studenski, R. Studies Into the Mechanism of Occupational 
Accidents. Przeglad Gorniczy (Engl. Trans.), v. 9. 1978. pp. 398-402. 

26. Suchman, E. A Conceptual Analysis of the Accident Pheno- 
menon. Social Problems, v. 8, No. 3, 1961, p. 241. 

27. Swain, A., and H. Guttman. Handbook of Human Reliabil- 
ity Analysis With Emphasis on Nuclear Power Plant Applications. 
Sandia Lab.. Albuquerque, NM, 1983. 700 pp. 

28. Theodore Barry and Associates. Fatality Analysis Data Base 
Development (contract S0110601). BuMines OFR 22-73. 1972. 253 
pp.; NTIS PB 219 250. 

29. U.S. Mine Safety and Health Administration. Mine Injuries 
and Worktime Quarterly. Jan-Dec. 1983. 1984. 34 pp. 

30. Mine Injuries and Worktime Quarterly, Jan. -Dec. 

1982. 1983, 18 pp. 

31. Mine Injuries and Worktime Quarterly. Jan. -Dec. 

1981. 1982, 18 pp. 

32. Mine Injuries and Worktime Quarterly. Jan.-Dec. 

1980. 1981, 18 pp. 



45 



CHAPTER 5.— INFORMATION DISPLAYS 




Information displays can be simple or complex. 



Humans receive information from the environment, 
process it, and take actions based on their judgments about 
the information; thereby making information central to 
everything they do. Information is received by humans 
either directly or indirectly. Directly perceived information 
would be involved when a shovel operator looks out his or 
her cab window and sees the position of the shovel over a 
haulage truck, or when an underground coal miner hears 
the creaks and groans of the roof "working." Although a 
great deal of information is received directly, we must often 
rely on indirect sources of information because some stimuli 
are beyond human sensing limits or can be sensed better 
or more conveniently if converted to another type of repre- 
sentation. Examples of indirect information include a sign 
warning of dangers that might not be perceived, a temper- 
ature gauge on a piece of equipment indicating the tem- 
perature of a fluid that cannot be seen or touched, a map 
showing the overall layout of an underground mine that 
could not be directly seen without removing 800 ft of over- 
burden and boarding an airplane, or a buzzer warning of 
a dangerous level of methane that cannot be sensed. 

The concern in this chapter is with the choice and design 
of indirect sources of information, i.e., information displays. 
A display, therefore, is considered to be any technique or 
process for presenting indirect information. The informa- 
tion can be conveyed through the visual, auditory, olfac- 
tory, or tactual senses. Because most information displays 
are visual and auditory in nature, this chapter will concen- 
trate on these types. 

CHOOSING A DISPLAY 

In evaluating various information displays for human 
use, several criteria are relevant. 

1. Speed at which humans can receive and process the 
information presented. 

2. Accuracy of interpretation. 

3. Speed in learning to use the display. 

4. Comfort. 

5. Absence of fatigue from long-term use. 

6. Performance level under degraded environments and 
stress. 



The choice and design of information displays that max- 
imize these criteria depend greatly on the type of task or 
tasks for which the information is required. People need 
information to perform the following seven generic tasks. 
Each task places unique demands on a display to present 
information in a manner that will facilitate its use. 

1. Quantitative reading. —Must determine a specific 
numeric value, such as pressure, weight, or speed. 

2. Qualitative reading.— Need only approximate a value, 
trend, rate of change, or direction of change. For example, 
an operator might only have to know that pressure is ris- 
ing or holding constant, but not the specific pressure value. 

3. Check-reading.— Compare one or more displays to a 
standard. For example, are the tensions on two lines equal? 

4. Setting an indicator.— Set an indicator to a desired 
value. For example, setting a timer to 90 s. 

5. Tracking.— Must follow or compensate for a continu- 
ously fluctuating stimulus. For example, maintaining a con- 
stant flow by opening and closing a valve in response to 
varying hydraulic pressures. 

6. Spatial orientations.— Must determine location in 
physical space. For example, determining where one is in 
a mine and how to get back to the lift. 

7. Receiving instruction or warning.— Must obtain infor- 
mation about how or why to do something. For example, 
a worker needs to know how many bags of rock dust to leave 
at each of five sites in a mine. 

It is common for a display to serve multiple purposes. 
An operator may have to read a specific value from display 
(quantitative), but may also need to know if there has been 
a change, over time, in the value and in what direction the 
change has occurred (qualitative). The same display may 
also be used for check-reading when comparisons are made 
with other similar displays. Further, the operator may have 
to use the information on the display to set an indicator, 
if it is out of tolerance. Such multiple-use situations present 
interesting tradeoffs for a designer of displays. A display 
designed for check-reading, for example, may not be opti- 
mum for quantitative reading or vice versa. 

A fundamental decision in display design is the choice 
of display mode, i.e., visual, auditory, olfactory, or tactual. 
Actually, in all but the most unusual circumstances, the 



46 



choice is between the visual and auditory modes. In general, 
visual displays are more appropriate than auditory displays 
when the information has the following characteristics: 

1. Long. 

2. Complex. 

3. Will be referred to later. 

4. Deals with locations in space. 

5. Does not call for immediate action. 

Visual information can usually be read and reread, and 
can be read at the receiver's pace. Auditory information, 
once presented, is usually gone and is presented at a pace 
set by the sender rather than by the receiver. 

Further, visual displays are more appropriate than aud- 
itory displays in the following situations: 

1. Auditory system of a person is overburdened with too 
many auditory information sources. 

2. The receiving location is too noisy. 

3. The receiver remains in one position rather than mov- 
ing about continually. 

Auditory displays, on the other hand, are more appro- 
priate than visual displays when the information has the 
following characteristics: 

1. Simple. 

2. Short. 

3. Will not be referred to later. 

4. Deals with events in time. 

5. Calls for immediate action. 

The best situations for auditory displays include the 
following: 

1. The visual system of a receiver is overloaded with too 
many visual displays. 

2. The receiving location is too bright or too dark for 
visual information to be seen. 

3. The information needs to be received regardless of the 
position of the operator's head, i.e., you do not have to look 
at an auditory display. 

As can be seen, auditory signals are especially appro- 
priate for presenting warnings that are usually simple, 
short, and require immediate action. 



VISUAL DISPLAYS 

Estimates are that humans receive as much as 90% of 
the information originating outside their bodies through 
their visual senses. How this information is presented is 
extremely important (7). 1 Advances in technology, including 
remote sensing devices, video displays, and even wristwatch 
televisions, hold both promise and challenge for the designer 
and user of future systems. The mining industry is mak- 
ing advances in the utilization of advanced technology, but 
for the most part still depends on the tried and true, 
"medium" technology equipment and displays it has used 
for years. There are some good reasons for this hesitation 
by the industry to embrace high-technology equipment. For 
one thing, currently designed mining equipment is rugged, 
lasts a long time, and is expensive to replace. In addition, 
it is used in some of the most inhospitable environments, 
which can adversely affect the reliability of some high- 
technology equipment 

The emphasis of this chapter, therefore, will be on the 
design of more traditional visual displays still being used 
and introduced in mining equipment. 



Quantitative Displays 

Quantitative displays are intended to convey to a user 
the specific numerical value of some underlying variable 
being measured by a device. This variable can be change- 
able, e.g., speed, pressure, flow; or it can be essentially static 
and unchanging, such as a ruler used to measure length. 

There are three basic types of quantitative displays: (1) 
fixed scale with moving pointer; (2) moving scale with fix- 
ed pointer; and (3) digital displays, also called counters. Ex- 
amples of these are shown in figure 5-1. There are strong 
indications that a digital display is usually superior to an 
analog display (moving pointer or moving scale) if a precise 
numerical value is required and if the value presented re- 
mains visible long enough to be read (12). But, if an operator 
were required to report a precise pressure value during an 
emergency where pressure was dropping rapidly, a digital 
display would not be the choice. Given ample opportunity 
to read the numerals on a digital display, however, both 
speed and accuracy can be greatly improved upon that ob- 
tained with a moving pointer display, as shown by the 
following data from Zeff (21 ): 



Digital display 

Circular, fixed scale, 
moving pointer 



Response time, s Errors 
0.94 0.5% 



3.54 



6.5% 



Fixed scale, moving pointer displays, however, are 
superior to digital displays for qualitative readings, such 
as when an operator needs to sense the direction or rate 
of change in a variable. In general, fixed scale, moving 
pointer displays are better than moving scale, fixed pointer 
displays; this is especially true when a control is used to 
set a value under the fixed pointer. The reason for this is 
that with a moving scale, fixed pointer, the scale has to 

1 FIXED SCALE, MOVING POINTER | 





40 50 60 TO 




Semicircular Vertical 
or curved 



MOVING SCALE, FIXED POINTER 



Decrease Increase 



Horizontal 



5 6 1 

_) 



Increase Decrrose 



40 50 

A 



Circular 



Open window Vertical 



DIGITAL DISPLAY I 



Humumu 



I2|7|9|4|g 
Counter 



3M578 



Electronic 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



Figure 5-1.— Examples of quantitative displays (12). (Courtesy of 

McGraw-Hill) 



47 



move in a direction opposite to that in which the values are 
changing. Look at the moving scale, fixed pointer vertical 
display shown in the middle row of figure 5-1. To increase 
the value, the scale must move down, yet "down" is usu- 
ally associated with decreasing values. The principal ad- 
vantage of moving scale, fixed pointer displays can be seen 
in the open window displays in the middle row of figure 5-1. 
Such displays take up a minimum amount of panel surface 
area, yet can display a very large range of values. Often, 
the scale is moved around spools behind the panel face. 

Design Features of Quantitative Displays 

Figure 5-2 illustrates several important concepts in the 
design of quantitative displays: 

1. Scale range.— The numerical difference between the 
highest and lowest value on a scale. 

2. Numbered value interval.— The numerical difference 
between adjacent numbers on a scale. 

3. Graduation interval value.— The numerical difference 
represented by adjacent graduation values. 

4. Scale unit value.— The smallest unit to which the scale 
is to be read. This may or may not correspond to the 
graduation-interval value. The scale in figure 5-2 is to be 
read to the nearest pound; therefore, 1 lb would be the scale 
unit value. 

The following design recommendations were gleaned 
from Bailey (i), McCormick and Sanders {12), and Oborne 
(13). 

Scale Markers 

It is generally considered a good design practice to pro- 
vide scale markers for every scale unit value. Figure 5-3 
illustrates the recommended dimensions for scale markers 
under both normal and low illumination conditions, assum- 



ing a viewing distance of 28 in. In some circumstances, plac- 
ing a marker at each scale unit produces a cluttered scale 
with inadequate space between markers. In such cases it 
is usually better to require an operator to interpolate be- 
tween markers. Interpolation to fifths yields satisfactory 
accuracy in many situations. 



Scale range 
(0-90lb) 




Graduation interva 
value (2 lb) 



Numbered 

value interval 

(10 lb) 



Figure 5-2.— Illustration of several numeric scale concepts. 



Basic sketches, measurements in inches 



Major scale marker 



HK 0.125 



CM 
CM 



r— Intermediate 

0, 2 5HV Cale mQrker 
rMo= 71 Minor scale 

i 1 ^ 1 



n 



marker- 



0.09 J 



Mill 




HH 0.05 

Hvlinimum separation between 
centers [could be 0.035] 



Major scale marker 

Intermediate scale 
marker 

Minor scale 



-H H— 0.035 [-Intermediate scale 

Tl* i marker 

■ 0.030HV ... , 

■ wv/ov Minor scale 

3|h h—0.025 I marker—, 

ill 1 1 III 1 1 1 1 



1 



o.io-J 



/ 



0.07 



Minimum separation between centers 



Actual Size 



milium 


milium 



B 



Figure 5-3.— Recommended format for quantitative scales under normal (A) and low (B) illumination conditions (adapted by McCor- 
mick (12) from reference 7). (Courtesy of McGraw-Hill) 



48 



If a normal viewing distance greater than 28 in is ex 
pected, the dimensions given in figure 5-3 must be increased 
to maintain the same visual angle to the observer. The 
following formula will correct the dimension of interest: 

Dimension at X in. = (dimension at 28 in.) x (X/28). 



Numerical Progression of Scales 

The numbered intervals on a scale should be in ones, 
twos, or fives, and multiples of 10. For example, 10-20-30, 
20-40-60, 50-100-150, or .5-1.0-1.5 would be acceptable. Pro- 
gression by threes, fours, and sixes should be avoided. 
Decimals make scales more difficult to use; but if used, the 
zero before the decimal should be omitted. 

Design of Pointers 

There is general agreement that pointers should— 

1. Have a tip angle of about 20°. 

2. Meet, but not overlap, the smallest scale marker. 

3. Be colored the same as the scale markings from the 
tip to the center, and be colored the same as the background 
from the center to the tail. 

4. Be as close to the dial face as possible to minimize 
parallax. 

Relative Importance of Design Features 

The effects of the following seven factors on speed and 
accuracy of dial reading (fixed scale, moving pointer) were 
assessed by Whitehurst (19): 

Numerical progression . . By 8 or by 10. 

Scale unit length 3.2 or 6.4 mm. 

Pointer width 6.4 or 0.8 mm. 

Marker width 0.8 or 1.6 mm. 

Scale number location . . . Same side as pointer 

or opposite side. 
Scale orientation Vertical or 

horizontal. 
Clutter Added words or 

nothing added. 

It was also found in this study that the two most im- 
portant factors affecting reading speed and accuracy were 
numerical progression (by 10 was better than by 8) and scale 
unit length. (The more widely spaced arrangement was bet- 
ter than the narrowly spaced arrangement.) The other fac- 
tors had little effect on performance. 

Qualitative Displays 

The task of a user in obtaining qualitative information 
from a display is to assess the appropriate value of some 
quantitative variable or to estimate its trend or rate of 
change. Often, the display that is best for obtaining a quan- 
titative reading is not the best for obtaining a qualitative 
reading. For example, three displays for the speed of mak- 
ing both qualitative readings (pointer above 60, say "high;" 
pointer 40-60, say "OK;" and pointer below 40, say "low") 
and quantitative readings were compared by Elkin (6). The 
three displays compared were an open-window fixed pointer, 
moving scale; and two moving pointer, fixed scales, one cir- 



cular and the other vertical. The results of this study are 
shown in table 5-1. The open-window display resulted in 
the fastest times for quantitative reading and the slowest 
times for qualitative reading. 



Table 5-1 .—Average times for qualitative and quantitative 
reading, with three types of scales (6), seconds 

(Courtesy of U.S. Wright Air Development Center) 



Type of scale 


Qualitative 


Quantitative 


Fixed pointer, moving scale: 

Open window 

Fixed scale, moving pointer: 

Circular 


115 

107 
101 


102 
113 


Vertical 


118 







If a quantitative scale can be divided into a limited 
number of zones or ranges, color coding or shape coding can 
be added to the dial to demarcate the regions, as shown in 
figure 5-4. Response time for three dial designs, two of which 
used coding techniques to represent danger zones, were com- 
pared by Kurke (11). The task was to respond when the 
pointer was in a danger zone. Figure 5-5 shows the designs 
and the relative response times using the uncoded display 
as the base (100%). As can be seen, a substantial decrease 
in response time is realized by the addition of simple color 
coding, and an even more dramatic decrease is effected by 
using the more complex wedge design. 

Check-reading an array of dials to determine if all con- 
ditions are normal is really just a special class of qualitative 
information seeking. Several persons have investigated ar- 
rangements of dials to facilitate such check-reading activi- 
ties, such as the study by Dashevsky (4). The general 
wisdom is that such dials should be arranged in neat rows 
and columns, with the normal positions of the pointers all 
aligned in the 9 o'clock or 12 o'clock position (4). This ar- 
rangement yields more accurate detection of deviant dials 
than if the normal positions are not consistent. It was found 
by Elkin (6), for example, that people made 350% more er- 
rors when the dials were subgrouped as shown in figure 5-6 
than when all the normal pointer positions were at 12 
o'clock. 





Normal 


Cold 


Normal 




(green) 
i 


(yellow) 
Caution \ 


(green) 


Caution 
(yellow)^ 






(yellow) >C3 


S\\ Hot 
/ V-^(red) 



Danger 
(red) 





Caution 



Figure 5-4.— Illustrations of coding methods for marking zones 
of instruments that are to be read qualitatively (12). (Counssyof 

McGraw-Hill) 



49 






A. No indication of 

"danger H zones 

(0-1,9-10) 

1 00 pet 



a. 



Red line indicating 
"danger" zones 



C. Red wedge appears 
when pointer is in 
"danger" zone 
74 pet 1 5 pet 

Mean time as percentage of condition A 



Figure 5-5.— Mean response time for detecting pointer in danger zone for three dial displays, where the mean response time is 
shown as a percentage of dial design. (Adapted by McCormick and Sanders (12) from reference 11, courtesy of McGraw-Hill) 



12 o'clock 
pattern 



Varied (subgroup) 
pattern 



© o © o 


G © Q 


o o o © 


© © 


o o o © 


Q © O 


© o o o 


O O © 


Figure 5-6.— Two patterns of 
a check-reading experiment. Tht 
in 350% more errors than did 


dials used by Dashevsky (4) in 
t subgroup arrangement resulted 
the 12 o'clock arrangement. 



SIGNAL AND WARNING LIGHTS 

Signal and warning lights are often used in the mining 
industry to indicate operation of equipment, such as con- 
veyors or vehicles, and to attract attention to a potentially 
dangerous situation, such as on an instrument panel or on 
a barricade around a newly dug hole. Unfortunately, there 
is little research relating to such signals, but some general 
conclusions can still be made. 

The detectability of a light depends on its size, lumin- 
ance (i.e., brightness), contrast with its background, and 
time available to detect it. A number of recommendations 
were offered by Heglin (8) regarding the use of signal and 
warning lights on instruments panels. 



When should they be used— To warn of actually or poten- 
tially dangerous conditions. 

How many warning lights. —Ordinarily only one. (If sev- 
eral warning lights are required, use a master warning or 
caution light and a word panel to indicate the specific 
danger condition.) 

Steady-state or flashing.— Because they are distracting, 
flashing lights should be reserved for emergencies. 

Flash durations.— If flashing lights are used, flash rates 
should be from 3 to 10 per second (4 is best), with equal in- 
tervals of light and dark. 

Warning-light intensity.— The light should be at least 
twice as bright as its immediate background. 

Light size.— The warning light should ordinarily be 1.5 
times the size of other indicators on a console. Master warn- 
ing or extreme emergency light should be twice the size of 
other console indicators. 

Location.— The warning light should be within 30° of the 
operator's normal line of sight. 

Color.— Warning lights are normally red because red 
means danger to most people. (Other signal lights in the 
area should be other colors.) 

An extension of the idea of using lights to warn is us- 
ing retroreflective material to draw attention to a poten- 
tial danger. Retroreflective material (or paint) contains 
minute glass spheres that return light directly back to the 
light source. The amount of light that is reflected to the eye, 
however, becomes less as the angle from the eyes to the ob- 
ject and from the object to the light source increases. A par- 
ticularly good application of retroreflective material is to 
make underground miners more visible to equipment oper- 
ators. The effect of various configurations of retroreflective 
material on detectability was tested by Beith, Sanders, and 
Peay (2). A one-fifth scale simulator was used in the study 
Dolls with miniature functioning caplamps and retroreflec- 
tive material on their helmets served as miners to be 
detected at various viewing angles in various body postures. 



50 



At the most severe viewing angle (i.e., 45° from the line 
of sight), probability of detection almost doubled when retro- 
reflective armbands and/or belts were added to the dolls. 



SIGNS AND LABELS 

Warning and information signs and labels are common 
in the mining industry and some are even mandated by the 
Code of Federal Regulations. Usually, signs convey impor- 
tant safety information or warn of potential hazards and 
dangers. It is important, therefore, that signs and labels 
be designed and displayed to maximize their effectiveness. 
Three attributes that are important in evaluating the ef- 
fectiveness of signs and labels are visibility, legibility, and 
comprehension. 

First, a sign or label must be seen and distinguished 
from its surroundings (visibility). The size, color, and place- 
ment of a sign or label are important determinants of visi- 
bility. Once a sign or label has attracted the attention of 
the viewer and has been seen, its alphanumeric or symbol 
characters must be easy to read or identify (legibility). This 
depends on such features as the size and form of the char- 
acters, and the contrast and illumination of the sign or label. 
Finally, the message presented must be understood by the 
viewer (comprehension). As will be seen, this can pose a real 
problem with pictorial-symbol signs. 

Typography 

Two important characteristics of alphanumeric charac- 
ters depicted in figure 5-7 are stroke width to height ratio 
and width to height ratio. Various stroke width to height 
ratios are illustrated in figure 5-8 for black letters on a white 
background and for white letters on a black background. 
Under good viewing conditions (normal illumination, no 
time constraint), most people can adequately discriminate 
alphanumeric characters over a wide range of stroke width 
to height ratios. Under adverse conditions, however, this 
variable becomes more important. The optimum ratio is 
smaller (i.e., thinner letters), for white characters on a black 
background (1:8-1:10) than for black characters on a white 
background (1:6-1:8). This is due to a phenomenon called 
irradiation in which white features appear to spread into 
adjacent black areas. 

Experimental evidence suggests that for capital letters, 
a width to height ratio of about 1:1 is optimum, but that 
it can be reduced to about 3:5 without serious loss in legibil- 
ity. In general, alphanumeric characters that have uniform 
stroke widths and strokes that do not have serifs (flourishes 
and embellishments) are more legible than fancy nontradi- 
tional styles. 

An important variable affecting legibility of a sign or 
label is the size of the characters or symbols used in rela- 
tion to the anticipated viewing distance. To be equally leg- 
ible, a sign or label must be made larger if it is moved 
farther from the viewer. A simple formula for determining 
the height of letters, given the viewing distance, importance 
of the sign or label, and illumination and reading condi- 
tions was developed by Peters and Adams (14). The formula, 
however, should probably not be applied to viewing dis- 



X - 



Stroke width to height = Z:Y 
Width to height = X'Y 

Figure 5-7.— Definition of stroke width to height and width to 
height ratios for alphanumeric characters. 



Stroke 

width to 

height 

ratio 


Black on white 


1 = 5 


ABC 


456 


l<6 


ABC 


-456 


1-8 


ABC 


-456 


I MO 


ABC 


456 


1 12 


ABC 


45 6 



White on black 



ABC 


456 


ABC 


45 6 


ABC 


456 


ABC 


456 


ABC 


45 6 



Figure 5-8.— Illustrations of stroke width to height ratios of let- 
ters and numerals (12). (Courtesy of McGraw-Hill) 



tances beyond 60 in, because the correction for importance 
and reading condition may be inadequate. The formula is 
as follows: 

H = 0.0022D + K, + K„ 

where H = height of letter, in, 
D = viewing distance, in, 
K, = correction factor for illumination and viewing 

condition; 

0.06 (abo\-e 1.0 fc, favorable reading 

condition), 

0.16 (above 1.0 fc, unfavorable reading 

condition), 

0.16 (below 1.0 fc, favorable reading conition), 

and 

0.26 (below 1.0 fc. unfavorable reading 

condition), 
and K 2 = correction factor for importance; 

0.075 for emergency and warning signs. 

0.000 for all other signs. 



51 



Table 5-2 uses this formula to compute letter heights for 
various representative viewing distances from 14 to 60 in. 
For viewing distances beyond 60 in, under varying illumina- 
tion conditions, letters on emergency signs should subtend 
approximately 30' of visual angle. Table 5-3 summarizes 
the recommendations. 



Table 5-2.— Recommended letter heights for labels and 
signs for various distance conditions, 1 inches 



14 



0.09 
.19 
.29 

.17 
.27 
.37 



28 



0.12 
.22 
.32 

.20 
.30 
.40 



48 



0.17 
.27 
.37 

.24 
.34 
.44 



60 



0.19 
.29 
.39 

.27 
.37 
.47 



Distance in. 

Unimportant, K 2 <0.0: 

K, <0.06 

K, <0.16 

K, <0.26 

Important, K 2 <0.075: 

K, <0.06 

K, <0.16 

Ki <0.26 

1 Based on formula by Peters (14). 



Table 5-3.— Recommended heights of letters on emergency signs 

Viewing distance, ft Letter height, in 

10 1.04 

20 2.08 

40 4.16 

100 10.44 




*Exit 72 pet 

No passageway, 
dead end 27 pet 



A 



Danger from rotating 

fan blades 47 pet 

♦Radiation hazard 

present 38 pet 

Fallout shelter 
location 1 4 pet 




*Eye wash location 68 pet 
Eye irritant 
located here 24 pet 



A 



•Corrosive hazard 71 pet 
2 1 pet 



Emergency hand 
wash location 



♦Correct interpretation 



Figure 5-9.— Examples of pictorial signs that caused confusion 
among mining industry employees. Most frequent interpretations 
are given below each figure with the percentage of subjects 
choosing each response given (3). 



of what it was intended to mean. Appendix C presents the 
pictorial warning signs recommended by Collins (3) for use 
in the mining industry, based on her tests of underground 
and surface mine employees. 



Pictorial Signs and Labels 

Although written signs and labels are probably the most 
commonly used method of providing safety and hazard in- 
formation, pictorial or symbolic signs are becoming more 
and more common in industry. The following advantages 
of pictorial signs over written signs were cited by Collins 
(3). They provide essential information— 

1. More rapidly, 

2. More accurately, 

3. At a greater distance, 

4. In less space, 

5. Without being language specific, and 

6. Without the need to read written language. 

All these advantages, however, do not come free. The 
development of pictorial signs that will be understood by 
a viewing population is a difficult task. For example, 72 
symbols to depict 40 different hazard and safety messages 
appropriate to the mining industry were developed. The 
comprehension of these symbols was tested among a diverse 
group of 271 underground and surface mine employees (3). 
Only 44% of the symbols were comprehended correctly by 
more than 90% of the people. More than 25% of the sym- 
bols were correctly comprehended by less than 75% of the 
people. Similar difficulties and results were obtained by 
Woo (20) in his evaluation of pictorial hazard signs on sur- 
face mobile mining equipment. Figure 5-9 shows a few ex- 
amples of pictorial signs that were not readily understood 
by the mining population tested by Collins (3). In some in- 
stances, workers interpreted the sign to mean the opposite 



AUDITORY DISPLAYS 

As pointed out at the beginning of this chapter, the 
auditory channel is especially effective for presenting warn- 
ing information. Such information is usually short, requires 
immediate action, and must be received by people even if 
they move about from one location to another. 

To be effective, auditory information must be detected 
by a listener. That is, an auditory signal must be heard 
above any background noises in an environment. If there 
is more than one auditory signal that must be responded 
to, then a listener must discriminate between them. In some 
cases, a listener must specifically identify a signal, such as 
identifying a sound as a sticky intake valve or a loose fan 
blade. 

In addition to discussing auditory alarms, the topic of 
speech communication is also addressed as a form of audi- 
tory display. 



Alarms 

There are numerous types of auditory alarms available 
today; table 5-4 lists some characteristics of various generic 
types. To insure that an alarm will be heard above an am- 
bient noise environment, the intensity of the alarm must 
be higher than the intensity of the noise. 

A procedure and rule of thumb for specifying the opti- 
mum intensity for a signal or an alarm was suggested by 
Deatherage (5). First, adjust the intensity of the signal un- 
til it is just barely detectable in the noise environment at 



52 



Table 5-4.— Characteristics and features of certain types of audio alarms (5) 

(Copyright 1972 by John Wiley and Sons, and reprinted by permission.) 



Alarm 


Intensity 


Frequency 


Attention 
getting 
ability 


Noise-penetration 
ability 


Diaphone (foghorn) 

Horn . 


Very high 


Very low 

Low to high 

. . do 

. .do 

do 

Medium to high 


Good 

. . do 

Good, if intermittent 

Very good if pitch rises 
and falls. 

Good 

. .do 

Fair 

Good, if intermittent 


Poor in low-frequency noise. 
Good. 


High 


Whistle 

Siren 

Bell 


. .do 

..do 

. . do 

Medium 

Low to medium 


Good, if frequency is 

properly chosen. 
Very good with rising and 

falling frequency. 
Good in low-frequency noise. 
Fair if spectrum is suited to 


Buzzer 


Low to medium 


Chimes and gong 

Oscillator 


..do 

Low to high 


. . do 

Medium to high 


background noise. 
Do. 
Good if frequency is properly 
chosen. 



normal operator work positions. Turn the noise off and 
measure the intensity of the signal at the entrance to the 
ear (called the masked threshold). Repeat this with several 
people and average the results. The rule of thumb is to set 
the intensity of the signal midway between the masked 
threshold and 110 dB. Thus, if a signal could just barely 
be heard in noise at 50 db, then one would be confident of 
its detection in noise if it were set at 80 dB. 

In addition to setting the intensity of a signal above the 
background noise level, the frequency of the signal can be 
selected to maximize its detectability. The idea is to select 
a signal frequency that corresponds to the lowest intensity 
frequency region of the background noise. Also, where possi- 
ble, it is best to select a signal frequency below the domi- 
nant frequency of the background noise; this is because loud 
noise of a given frequency tends to mask signals higher than 
its frequency more than it masks signals lower than its 
frequency. 

Under some conditions, especially those involving very 
high intensity noise, the use of hearing protectors can in- 
crease the detectability of a signal. This occurs because the 
hearing protection brings the noise and signal intensity 
down so that the signal can be more easily detected. 

McCormick and Sanders (12) provided the following list 
of general design recommendations for auditory warning 
and alarm signals which were gleaned from various sources: 

Use frequencies between 200 and 5,000 Hz, and preferably 
between 500 and 3,000 Hz, because the ear is most sensitive 
to this middle range. 

Use frequencies below 1,000 Hz when signals have to 
travel long distances (over 1,000 ft), because high frequen- 
cies do not travel as far. 

Use frequencies below 500 Hz when signals have to "bend 
around" major obstacles or pass through partitions. 

Use a modulated signal (1 to 8 beeps per second or 
warbling sounds varying from 1 to 3 times per second), 
because it is different enough from normal sounds to de- 
mand attention. 

Use signals with frequencies different from those that 
dominate any background noise to minimize masking. 

If different warning signals are used to represent different 
conditions requiring different responses, each should be 
discernible from the others, and moderate intensity signals 
should be used. 

Where feasible, use a separate communication system for 
warnings, such as loudspeakers, horns, or other devices, not 
used for other purposes. 



It should be pointed out that some of these recommen- 
dations can create conflicting situations. For example, 
because mining noise tends to be of low frequency, it would 
be best to use a high-frequency signal, despite the fact that 
high frequencies do not carry as far as low-frequency sounds. 

Speech 

Speech is the most common method for transmitting in- 
formation between humans. With the development of reli- 
able, inexpensive speech synthesis and recognition systems, 
it may also become a common method for transmitting in- 
formation between humans and machines. Speech is one 
of the most complex, yet suitable forms of communication. 
Although there are only about 40 speech sounds in the 
English language, these can be put together to convey the 
most complex of messages. 



Intensity of Speech 

Different speech sounds have different levels of speech 
power (intensity). In general, the vowel sounds contain more 
speech power than do the consonant sounds. The a as pro- 
nounced in talk has approximately 680 times the speech 
power of th as pronounced in then. Unfortunately, the less 
powerful consonant sounds are the most important for 
understanding speech. 

The overall intensity of speech, of course, varies from 
person to person. The following, however, are representative 
intensities averaged over large samples of speakers: 

Talking as softly as possible 46 ABA 

Lecture or telephone conversation 66 ABA 

Talking as loudly as possible 86 ABA 



Intelligibility of Speech 

Intelligibility is the extent to which a spoken message 
is understood by a listener. How much of a message is under- 
stood depends, among other things, on the nature of the 
message and the expectation of the listener. The English 
language is very redundant: one does not have to hear every 
syllable to understand a word, nor even - word to understand 
a sentence. Further, if a listener has some idea about what 
a message will pertain to. the probability of understanding 
the message increases. 



53 



In the mining industry, speech communication often 
takes place in noisy environments, such as processing 
plants, or near large mining machines. Intelligibility under 
such conditions is of critical importance for maintaining pro- 
ductivity and safety. One way to increase intelligibility, 
especially in the presence of noise, is to limit the size of the 
vocabulary and make a list of words known to both the 
listener and speaker. Rather than use them interchange- 
ably, one of several words to mean the same thing, agree 
on one term and use it consistently. For example, the words 
"increase," "raise," "up," "advance," "augment," and "in 
tensify" can all mean the same thing. Rather than use them 
interchangeably, one word should be selected and used con- 
sistently. When selecting standard vocabulary words, 
consider potential confusion between words. For example, 
rather than using "increase" and "decrease," it would be 
better to use "raise" and "lower" because they are less 
likely to be confused in a noisy environment. 

In general, complete sentences have higher levels of in- 
telligibility than do single words, and long words are more 
intelligible than short words. Words commonly used every 
day are more intelligible than uncommon words. A classic 
example of increasing the length of a word to increase its 
intelligibility is the use of the International Word-Spelling 
Alphabet. Rather than telling a mechanic to get part 
number ABE-136, one would say "Alpha-Bravo-Echo-one- 
three-six." In a noisy environment, ABE is easily confused 
with APE. 

Preferred Octave Speech Interference Level (PSIL) 

This index, reported by Peterson and Gross (15), gives 
a rough evaluation of the effect a noisy environment has 
on the transmission of speech. It is relatively easy to assess 
and compute if the right equipment is available. A sound 
pressure meter is needed that can measure intensity (sound 
pressure in decibels) in three octave bands centered at 500, 
1,000, and 2,000 Hz. The PSIL is simply the average of the 
decibel levels of the noise in the three octave bands. This 
technique is appropriate where the noise is relatively con- 
tinuous and its spectrum (intensity at various frequencies) 
is relatively flat. Given the PSIL, table 5-5 can be used to 
determine the maximum distance that two people can be 



Table 5-5.— Maximum distance between speaker and 

listener to carry on a satisfactory conversation in various 

intensity voices under ambient noise conditions defined by 

the preferred octave speech interference level (PSIL) (18), feet 

(Courtesy of National AcaHemv Press) 



PSIL, 
dB 

40 

45 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

105 

110 

120 

NAP Not applicable. 



Normal 



32 
16 

8 

5 

3 

1.75 
.75 
.5 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 



Raised 



>32 

32 

17 

10 

6 

3 

2 

1 

.5 

NAp 

NAp 

NAp 

NAp 

NAp 

NAp 

NAp 



Very 
loud 



>32 
>32 
>32 

23 

12 

7 

3.5 

2 

1 

.6 

NAp 

NAp 

NAp 

NAp 

NAp 

NAp 



Shout 



>32 
>32 
>32 
>32 

24 
13 

7 

4 

2 

1.25 
.75 
NAp 
NAp 
NAp 
NAp 
NAp 



Max vocal 
effort 



>32 
>32 
>32 
>32 
>32 
>32 
>32 
30 
16 

8 

5 

3 

1.5 

1 
.5 
NAp 



apart and converse in a normal voice, raised voice, very loud 
voice, or shouting voice. These limits represent distances 
where 98% of the speech would be heard. Thus, in a proc- 
essing plant where the PSIL was 80 dB, two people could 
converse in a raised voice at 0.5 ft apart, in a very loud voice 
at 1 ft, in a shouting voice at 2 ft, and with maximum vocal 
effort at 16 ft. 

Hearing Protection and Speech 

It was found by Howell and Martin (9) that hearing pro- 
tection did not degrade speech intelligibility for a listener. 
This was confirmed in high-noise environments (90 dBA), 
but a decrease in intelligibility in low-noise (70 dBA) envi- 
ronments was found (1 7). Reference 9, however, found that 
if those talking wore hearing protection, their speech was 
reduced in both intensity and quality, and intelligibility ac- 
tually decreased for the listener. The lesson here is that, 
in noisy situations where people wear hearing protection, 
extra effort must be made to speak loudly and clearly. Peo- 
ple will think they are speaking more loudly than they 
really are, and therefore must be made aware of this to com- 
pensate for their misperceptions. 

Underground Loudspeaker System: A Case Study 

Results of adding a loudspeaker telephone system to an 
underground longwall coal face in the Netherlands were 
reported by Koene and Ruwette (10). The particular face 
was approximately 790 ft in length with a working height 
of approximately 3 ft. The face was equipped with the follow- 
ing communication systems prior to installation of the 
loudspeaker phones: 

1. Dial telephones at the ends of the face. 

2. Telephone sets at a number of points on the actual coal 
face. (Face lights were flashed to signal a call, but there 
was no way to determine which telephone should be 
answered or who was being called.) 

3. Elaborate signaling by flashing the face lights. 

4. Messages transmitted verbally from person to person. 
The loudspeaker telephones were installed every 60 to 

70 ft. Each set incorporated two loudspeakers and a micro- 
phone. Pressing of the microphone switch enabled transmis- 
sion of a message through all the loudspeakers on the coal 
face. A whistle signal could also be transmitted. 

Problems During Introduction of the System 

Koene and Ruwette (10) also indicated the following 
social-psychological communications problems caused after 
the system was installed: 

1. Personnel were initially timid about using the system. 

2. Because of the public nature of the communications, 
greater control of language, criticism, and negative remarks 
was required. 

3. Supervisory staff had a tendency to intervene when a 
lower ranking supervisor gave an instruction, thereby 
undermining his or her authority. 

4. There was a temptation to transmit messages encourag- 
ing workers to work harder. This reduced the credibility 
of the system. 

5. The system was used like a regular telephone; the per- 
son to whom the message was addressed was required to 
reply. 

6. Supervisors sought more information than was needed 
to conduct proper operations. 

These investigators indicate that, with proper instruc- 
tion, these initial problems were reduced or eliminated. 



54 



Results of Installation 

With the loudspeaker system, one supervisor did the 
work of the two required before the system was installed. 
This was accomplished without increasing the distance 
traveled by the supervisor to perform the job. The major 
finding was that after installation, the duration of stoppages 
per shift decreased from 160 to 128 min, a reduction of 20%. 
Compared with all coal faces in the mine, the test site had 
a lower percentage of utilization rate before installation (i.e., 
percentage of time coal was being extracted). After installa- 
tion, the percentage of utilization was higher than the over- 
all mine average. There was clear evidence that the system 
reduced the duration of stoppages by supplying necessary 
information to everyone along the coal face. Better coordina- 
tion of material transport and repositioning of props reduced 
the number and duration of sucb stoppages. Response times 
to emergencies were significantly reduced, and the 
responses were more coordinated. 



OLFACTORY DISPLAYS 

Although olfactory displays are not very common, there 
are applications where their use can be beneficial. In facil- 
ities served by natural gas, for example, an odorant is added 
to the naturally odorless gas to aid in the detection of leaks. 
Another example of an olfactory display is the use of stench 
systems in underground noncoal mines to warn of a fire or 
other emergency. Miners, upon smelling the stench, evac- 
uate the mine according to a prearranged plan. 

Stench systems have been used for 60 yr in underground 
mines. The odorant most commonly used, ethyl mercaptan, 
however, is highly toxic and sometimes causes nausea 
among the miners. In 1980, the Bureau embarked on a pro- 
gram to develop an improved stench system (16). The 
chemical tetrahyprothiophane (THT) was selected as the 
odorant; it is widely used in Europe as a natural gas odorant 
and is not as toxic as ethyl mercaptan. In a field test of the 
new system, which included a new method for dispersing 
the odorant, average penetration time (time from release 
to detection at various locations within the mine) was 10.5 
min compared to 19.6 min using the old system, a reduc- 
tion of 46%. 

DISCUSSION 

Information is critical for safe, productive work; it is 
necessary for guidance of decisionmaking and actions. Many 
sources of information are not readily available so indirect 
sources of information are relied on— information displays. 
This chapter has reviewed some human factors considera- 
tions in the design of medium-technology visual and audi- 
tory displays, signal lights and signs, and has illustrated 
that speed and accuracy are affected by how these infor- 
mation sources are designed. 

Although high-technology computer displays were not 
dealt with, as their use in mining is still relatively small, 
many of the same principles of design apply. Concern with 
detectability, legibility, and comprehension still remain. 
With many computer displays, information overload often 
is an additional problem. Operators are presented with a 
screen full of numbers and are expected to analyze and in- 
terpret the meaning of the information presented. Much can 
be done to improve such displays, including presenting only 
the information the operator really needs to do the tasks, 



use of color coding, and proper layout of information on the 
screen. The human factors literature has really only 
scratched the surface with regard to formatting computer- 
displayed information. It is anticipated that in the future 
more guidance on proper designs will be available. Until 
then, as with other medium-technology displays, existing 
human factors can be applied, keeping in mind the infor- 
mation needs of the operator, supplying neither less nor 
more than is required, and trying to do so in a manner that 
requires the least amount of mental processing. 



REFERENCES 

1. Bailey, R. Human Performance Engineering: A Guide for 
System Designers. Prentice Hall, 1982, 672 pp. 

2. Beith, B., M. Sanders, and J. Peay. Using Retroreflective 
Material to Enhance the Conspicuity of Coal Miners. Human Fac- 
tors, v. 24, No. 6, 1982, pp. 727-735. 

3. Collins, B.L. Use of Hazard Pictorials/Symbols in the Minerals 
Industry (contract J0113020, NBS). BuMines OFR 44-84, 1983, 193 
pp.; NTIS PB 84-165877. 

4. Dashevsky, S. Check-Reading Accuracy as a Function of 
Pointer Alignment, Patterning, and Viewing Angle. J. Appl. Psych., 
v. 48, 1964, pp. 344-347. 

5. Deatherage, B. Auditory and Other Sensory Forms of Infor- 
mation Presentation. Ch. in Human Engineering Guide to Equip- 
ment Design, ed. by H. Van Cott and R. Kinkade. Wiley, 1972. pp. 
123-160. 

6. Elkin, E. Effect of Scale Shape, Exposure Time and Display 
Complexity on Scale Reading Efficiency. U.S. Air Force Wright 
Air Devel. Center, Dayton, OH, TR-58-472, 1959, 142 pp. 

7. Grether, W., and C. Baker. Visual Presentation of Informa- 
tion. Ch. in Human Engineering Guide to Equipment Design, ed. 
by H. Van Cott and R. Kinkade. Wiley, 1972, pp. 41-122. 

8. Heglin, H. NAVSHIPS Display Illumination Design Guide. 
Volume II: Human Factors. U.S. Naval Electronics Lab Center, 
San Diego, CA, NELC/TD223. 1973, 313 pp. 

9. Howell, K., and A. Martin. An Investigation of the Effects of 
Hearing Protectors on Vocal Communication in Noise. J. Sound 
and Vibration, v. 41, 1975, pp. 181-196. 

10. Koene, G., and L. Ruwette. Communication at the Coal Face. 
Eur. Coal and Steel Community, Ergonomic Res.. Doc. 97 70e RCE. 
1970, 52 pp. 

11. Kurke, M. Evaluation of a Display Incorporating Quantitative 
and Check-Reading Characteristics. J. Appl. Psych., v. 40. 1956. 
pp. 233-236. 

12. McCormick, E., and M. Sanders. Human Factors in Engineer- 
ing and Design. McGraw-Hill. 5th ed., 1982, 615 pp. 

13. Oborne, D. Ergonomics at Work. Wiley, 1982. 321 pp. 

14. Peters, G., and B. Adams. The Three Criteria for Readable 
Panel Markings. Product Eng.. v. 30, No. 21. 1959. pp. 55-57. 

15. Peterson, A., and E. Gross. Handbook of Noise Measurement. 
General Radio Co., Concord. MA, 8th ed., 1978. 322 pp. 

16. Pomroy, W.. and T. Muldoon. A New Stench Gas Fire Warn- 
ing System. Pres. at 52nd Annual Tech. Session of the Mine Acci- 
dent Prevention Assoc, of Canada. Toronto. Canada. May 25-27. 
1983, pp. 83-91. 

17. Prout, J.H.. P.L. Michael, and L.W. Saperstein. A Study of 
Roof Warning Signals and the Use of Personal Hearing Protection 
in Underground Coal Mines (grant G0133026. PA State Univ.i. 
BuMines OFR 46-74, 1973, 238 pp.: NTIS PB 235 S54 

18. Webster, J. Effects of Noise on Speech Intelligibility. Am. 
Speech-Language-Hearing Assoc., Rockville. MD. ASHA Rep. 4. 
1969, 16 pp. 

19. Whitehurst, H. Screening Designs Used To Estimate the 
Relative Effects of Display Factors on Dial Reading. Human Fac- 
tors, v. 24, No. 3. 1982. pp. 301-310. 

20. Woo, J. Perception of Hazard Pictorials on Surface Mobile 
Mining Equipment. Trans Systems Co.. Vienna. VA. 19S0. 174 pp. 

21. Zeff, C. Comparison of Conventional and Digital Time 
Displays. Ergonomics, v. 8. No. 3. 1965. pp. 339-345. 



55 



CHAPTER 6.— DESIGN OF CONTROLS, EQUIPMENT, AND TOOLS 




Because of the unique operating requirements and environments of mining equipment, special attention must 
be given to human factors considerations, whether in the design of operating controls, tools and access for 
maintenance, or the equipment itself 



In this chapter a broad overview of major human fac- 
tors considerations and issues in the design of controls, 
equipment, and tools will be presented. The benefits to be 
gained by incorporating human factors into the design of 
equipment, include increased safety, higher productivity, 
and worker satisfaction and comfort. Special attention will 
be given to the problems of seating on low-seam under- 
ground equipment, restricted field of vision in underground 
and surface equipment, egress and ingress in surface equip- 
ment, and designing for ease of maintenance in all types 
of mining equipment. 



CONTROLS 

Controls are the means by which humans communicate 
with equipment, and the proper design of controls helps en- 
sure safe, productive operation of that equipment. The Min- 
ing Equipment Safety Laboratory of the Mine Safety and 
Health Administration (MSHA) analyzed all fatal accident 
reports involving underground coal mine mobile and elec- 
trical face equipment for the years 1972 through 1979 (17)} 
A total of 350 fatalities were investigated. Twenty-five 
fatalities (an average of three per year) were attributed to 
improper control design. Unknown is the number of non- 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



fatal injuries caused, in whole or in part, by improper con- 
trol design. It must be assumed, however, that it is higher 
than the number of fatalities. 



Types of Controls 

There is a wide variety of control devices available, with 
certain types best suited for particular applications. Com- 
mon control types were classified by McCormick and 
Sanders (20) as to the type of information they can most 
effectively transmit (discrete vs continuous) and the amount 
of force normally required to manipulate them (large vs 
small). Discrete information is information that can only 
represent one of a limited number of conditions, such as on- 
off; high-medium-low; crusher 1, crusher 2, crusher 3; or 
alphanumerics, such as A, B, and C; 1, 2, and 3. Continuous 
information, on the other hand, can assume any value on 
a continuum, such as speed (as to 60 mph); pressure (as 
1 to 100 psi); or direction of motion. Table 6-1 lists the com- 
mon types of controls classified by this scheme. Figure 6-1 
illustrates some of the more common of these controls. 

It is important that the type of control used be suited 
to the type of information an operator wishes to communi- 
cate to the equipment. For example, speed is generally 
thought of as a continuous variable. Going slow or fast is 
thought of as slowing down or speeding up; yet many pieces 
of underground electrical equipment permit an operator to 



56 




Toggle 


Toggle 


Rotory 


switch 


switch 


selector 


2- 


3- 


switch 


position 


position 


2 



Knob 




For transmitting discrete information 



Foot push- 
button 



For transmitting continuous information 

CranK Wheel Lever 



'Si 




Pedal 




Figure 6-1.— Common types of controls classified by type of 
information they transmit most effectively (20). (Courtesy of 



McGraw-Hill 



Table 6-1 .—Common types of controls, 

by type of information transmitted 
and force required to manipulate (20) 



Information 
transmitted 

Discrete: 
Pushbuttons, including keyboards 

Toggle switches 

Rotary selector switches 

Detent thumb wheels 

Detent levers 

Large hand pushbuttons 

Continuous: 

Rotary knobs 

Multirotational knobs 

Thumbwheels 

Levers or joysticks 

Small cranks 

Handwheels 

Foot pedals 

Large levers 

Large cranks 



Manipulation 
force required 



Small. 

Do. 

Do. 

Do. 
Large. 

Do. 



Small. 

Do. 

Do. 

Do. 

Do. 
Large. 

Do. 

Do. 

Do. 



(Copyright 1982 by McGraw-Hill, and reprinted by permission) 



control speed only as a discrete variable: on-off. Slow speed 
is achieved by repeatedly activating the tram controls to 
inch the machine forward. 



Factors in Control Design 

Although controls differ in design, there are certain fac- 
tors that apply to all types of controls and influence the 
overall performance of an operator. Well-designed controls 
that match the task requirements, and the capabilities and 
limitations of an operator are easier to learn to operate, are 
operated faster and more accurately, and result in fewer 
errors and better operator acceptance. The major factors 
that should be considered in the design or selection of con- 
trols are identification, control-response ratio, resistance, 
deadspace, and backlash. Spacing and general positioning 
of controls are discussed in another section of this chapter 



Identification of Controls 

The ability to quickly and accurately identify the proper 
control can often mean the difference between life and 
death, especially in the mining environment where massive 
pieces of equipment are set in motion with the flick of a 
lever. An operator, while reaching for a boom-sump control 
on a roof bolter machine, could accidentally activate the 
boom swing and crush a person against a mine rib. Identi- 
fication of the proper control is really a problem of control 
coding, and the basic methods of control coding are shape, 
texture, size, location, color, and labels. 

The choice of a coding technique and the specific coding 
values depend on the speed and accuracy requirements of 
a task, whether an operator can look at the controls, what 
the environmental conditions are (especially illumination), 
whether an operator is wearing gloves, and the number of 
controls that must be coded. 

The most common method of control coding used on min- 
ing equipment is location coding. For example, on one par- 
ticular model of a machine, the tram control is third from 
the outside, the boom swing is second from the outside, etc. 
Two deficiencies, however, are often present in mining 
equipment, which minimize the effectiveness of location 
coding. First, there is often no standardization in control 
placement from manufacturer to manufacturer, or even 
from model to model within a manufacturer's line. Second, 
controls are often very close together and are easily con- 
fused. A good example of this is shown in figure 6-2. Some 
manufacturers provide long and short lever controls, or bend 
levers so that the controls are positioned in different planes 
for easier discrimination as shown in figure 6-3. 

Shape coding involves providing different shaped 
handles or knobs on the equipment. Figure 6-4 shows a case 
where operators had added a glob of electrical tape to one 
handle in an array of handles to aid in identification; an 
example of primitive shape coding. The shapes selected for 
shape coding must be different enough from one another 
to be identified by operators even when they are wearing 
gloves. Figure 6-5 presents a set of shapes that have been 
found by the U.S. Army to be identifiable by touch alone 
even when wearing gloves (30). Further, to facilitate the 
learning of a control function, it is helpful if the shapes 
selected connote, or relate to, the function being controlled. 
The shapes shown in figure 6-6 for the controls of roof 
bolting machines were suggested based on opinions of 
MSHA inspectors and equipment manufacturers (15). 

One consideration often overlooked in the use of shape 
codes is that of maintenance. If a control knob can be 
removed or easily broken, it may be replaced by a dissimilar 
knob, thus destroying the coding scheme. The welding of 
knobs to control levels to prevent this problem is usually 
a good idea. 

Coding by texture (i.e., smoothness, rippledness. or 
knurledness) and size is somewhat limited with respect to 
the number of different values that can be detected. Size 
coding probably has more application in the mining environ- 
ment than texture coding because of the tendency of some 
texture codes to become obliterated by dirt and muck and 
the difficulty of identifying textures when wearing gloves. 
If size coding is being used, probably no more than three 
sizes should be employed. The largest size should be for 
either the most frequently used or the most important 
controls. 



57 




Figure 6-2.— Control station of a low-seam coal auger. 




Figure 6-3.— Controls with different length lever controls, which provides easier location discrimination. 



58 




Figure 6-4.— Example of operator-provided shape coding. Electrical tape has been added to the fourth knob from the left to aid 
in identifying the control. 



e 




Figure 6-5.— Control knob shapes that are easily identified by touch while wearing gloves (30). (Courtesy of us Army mbs* Command) 



59 



Drill rotate 




Canopy 



r^^n 




Auger clamp 
or drill guide 




Boom lift 



Boom swing 



Cable reel 





Stabjack 



Boom sump 



Bolt torque 



Figure 6-6.— Control shapes recommended for underground 
roof bolter (15). 



Coding by colors and labels requires visual confirma- 
tion of the control choice. Operators do not often have the 
luxury of looking at the controls each time they have to 
activate them. One thing that everyone agrees on, however, 
is that, at a minimum, every control (and display for that 
matter) must be labeled. With labels, an operator can at 
least determine the function of a control if the function has 
been forgotten, although it is unlikely that an operator 
could rely on labels as the primary coding method during 
actual operation of the equipment. 

If color coding is used, as for example on a control panel 
in a processing plant, it is important that the colors chosen 
are easily identified and that their meaning is the same 
everywhere in the plant. For example, if a red pushbutton 
means stop on one panel, it should not mean energize on 
another panel. 

A well thought out coding scheme is especially impor- 
tant for complex equipment used in the mining industry. 
Inadvertent activation of the wrong controls can be reduced 
and often eliminated by the prudent application of control 
coding techniques. 

Control-Response Ratio 

The control-response (C-R) ratio is the ratio of the move- 
ment of a control device to the movement of a system 
response. A large C-R ratio would indicate that a control 
must be moved a large distance to cause a small system 
response. A small C-R ratio indicates that a small control 
movement results in a large system response. 

Often, the problem with C-R ratios is that they are too 
small; that is, a slight movement of a control may cause 
a large swing of a boom conveyor or an abrupt increase in 
tram speed. Such controls are difficult and dangerous to use. 
One solution that is gaining acceptance is the use of pro- 
portional controls to replace the detent on-off controls com- 
monly found in underground hydraulic equipment. An ex- 
ample of a proportional control is the accelerator pedal in 



an automobile; the more you depress the pedal, the faster 
you go. 

The proper C-R ratio must be empirically determined 
by testing various ratios and determining the speed and ac- 
curacy of system control achievable with each ratio. 

Resistance 

There are several types of resistance that are inherent 
in, or can be built into, controls. The main types are listed 
in table 6-2. In general, a little elastic resistance is usually 
desirable, but inertial resistance often causes a decline in 
control precision. 

Table 6-2.— Description of common types 
of control resistance 

Type Description 

Elastic Spring loaded— the greater the displacement of 

a control, the greater the resistance. 

Static Resistance to initial movement is maximum but 

drops off sharply as a control is moved 
(sticky). 

Coulomb Continued resistance to movement that is 

unrelated to the velocity or displacement of a 
control movement. Resists change in direction. 

Viscous damping .... Like moving a spoon through thick syrup. The 
faster one moves a control, the more 
resistance is encountered. Resists quick 
changes in direction and helps execute 
smooth control movements. 

Inertia Resistance to movement or change in direction 

caused by the mass of the mechanism. 
Resists quick control movements and any at- 
tempt to slow down or speed up control 
movements. 

Deadspace 

Deadspace in a control mechanism is the amount of con- 
trol movement around the null position that results in no 
response of the device being controlled. A little deadspace 
is usually desirable, especially if vibration and buffeting 
of an operator are present. Too much deadspace, however, 
can be detrimental to operator performance. 

Backlash 

As described by McCormick and Sanders (20), the best 
way to think of backlash is to imagine operating a joystick 
or lever with a loose, hollow cylinder fitted over it. When 
the cylinder is moved to the right, for example, it touches 
the stick on the left. If you move the cylinder to the right 
and then reverse direction, the stick does not start to return 
to the left until the cylinder comes up against the right side 
of the stick. Until the cylinder contacts the stick, the oper- 
ator's control movements have no effect on the system. In 
essence, then, backlash is deadspace at any control position. 

Backlash is usually inherent in any system that uses 
gears, because the gear teeth rarely mesh perfectly. When 
a direction of movement is changed, there is a delay until 
the gear teeth contact the opposite side of the gear-teeth 
slots. Typically, operators do not handle backlash well, and 
performance deteriorates with increasing amounts of it. 

Design of Specific Controls 

There are several good sources of design recommenda- 
tions for common controls, such as knobs, levers, cranks, 



60 



pedals, and wheels (8, 30, 32, 35). No attempt will be made 
here to set forth all the detailed recommendations contained 
in these sources. Appendix D, however, presents recom- 
mended sizes, displacements, and resistances for many of 
the common controls, including pushbuttons, toggle 
switches, rotary selector switches, cranks, levers, and 
pedals. 



EQUIPMENT DESIGN 

The focus of this section is on the integration of controls 
and displays, and the layout of workstations, as aspects of 
equipment design. In addition, some special problems will 
be addressed, including operator field of vision, egress and 
ingress, and designing for maintenance. 

The proper design of equipment that matches the capa- 
bilities and limitations of an operator, and provides the in- 
formation and control functions needed by the operator to 
perform a task will pay dividends over and over. Reduced 
training time, less downtime, higher quality work, fewer 
errors and accidents, and greater user satisfaction accrue 
from well-designed equipment. The importance of such con- 
siderations is stressed by Grandjean (11) and U.S. Air Force 
Systems Command (29), for example. 

There is a general misconception that people are adapt- 
able; they can get used to anything. As with most mis- 
conceptions, there is probably a grain of truth buried 
somewhere in them. People are adaptable, but there is a 
cost associated with forcing them to adapt. It takes energy, 
both physical and mental, to adapt to the unfamiliar or 
unexpected, and this leads to both physical and mental 
fatigue— the ultimate consequences of which are obvious. 

Consider the tradeoffs: Properly design a machine once 
or require every operator who uses it to accommodate and 
adapt. It is not easy but it is necessary to design equipment 
so that (1) controls operate as expected, (2) operators can 
reach controls and see displays, and (3) enough space ex- 
ists to carry out the work in a safe and efficient manner. 

Compatibility 

Probably one of the most fundamental human factors 
design principles is to design to meet user expectations. 
Equipment should work in a natural, expected manner; that 
is, it should be compatible with a user's expectations. 

There are several types of compatibility: conceptual com- 
patibility, movement compatibility, and spatial compatibil- 
ity. As pointed out by McCormick and Sanders (20), some 
compatible relationships are intrinsic in certain situations. 
Turning a wheel to the right in order to turn to the right 
is an example. Other compatible relationships are culturally 
acquired. In the United States, for example, a light switch 
is usually pushed up to turn it on, but in certain other coun- 
tries it is pushed down. 

Conceptual Compatibility 

Conceptual compatibility deals with the meaning of 
symbolic information. For example, red means stop and 
green means go. This type of compatibility is most relevant 
for the design of coding systems and symbolic signs. 

Movement Compatibility 

Movement compatibility refers to the direction of con 
trol movement and the resultant system response. An ex 



ample is turning a steering wheel to the right to cause a 
vehicle to turn right. Figure 6-7 shows compatible relation- 
ships for dial movement and display response where both 
the dial and the display are in the same plane. The situa- 
tion becomes more complicated when the control and the 
display are in different planes as shown in figure 6-8. Both 
figures 6-7 and 6-8 represent directions of motion that a 
majority of people would expect without prior training or 
experience (i.e., population stereotypes). The expectation is 
stronger in some cases than in others. Figure 6-9 presents 
common meanings associated with lever movements in dif- 
ferent planes and directions. Lever controls are very com- 
mon on underground and surface mining equipment; yet, 
compatible relationships often are not observed. For exam- 
ple, up-down movement of a lever may cause a boom to 
swing left-right. Table 6-3 presents a list of common move- 
ment stereotypes grouped by function, without regard for 
spatial layout. 

Table 6-3.— Compatible directions of movement 
associated with various control functions (30) 

Function Direction 

On Up. right, forward, clockwise, pull (push-pull type 

switch). 

Off Down, left, rearward, counterclockwise, push. 

Right Clockwise, right. 

Left Counterclockwise, left. 

Raise Up. back 

Lower Down, forward. 

Retract Up, rearward, pull. 

Extend Down, forward, push. 

Increase Forward up, right, clockwise 

Decrease Rearward, down. left, counterclockwise. 

Open valve Counterclockwise. 

Close valve Clockwise. 

(Courtesy of US Army Missile Command) 




A 

► 



t 





Figure 6-7.— Movement compatibility relationships where dial 
and display are in same plane. 



61 




Figure 6-8. — Compatible control-display movements when con- 
trols and displays are in different planes (11). (Courtesy of Taylor and 

Francis Ltd.) 



Backward 

Less 

Minus 

Off 

Up 



Forward 

More 

Plus 

On 

Down 



Left 


Right 


Less 


More 


Minus 


Plus 


Off 


On 




Left 


Right 


Less 


More 


Minus 


Plus 


Off 


On 



Down 

Less 

Minus 

Off 

Backward 



Figure 6-9.— Common meanings of lever movements (adapted 

from 11). (Courtesy of Taylor and Francis Ltd.) 



Spatial Compatibility 

Spatial compatibility refers to the physical location and 
relationship between the controls and the displays they con- 
trol. Figure 6-10 shows examples of arrangements of con- 
trols and displays. Where the relationship between controls 
and displays is not obvious, it is more likely that the wrong 
control will be activated, user response time will be slowed, 
and additional training time will be required to learn how 
to operate the equipment. 

Placement of Displays and Controls 

To determine display and control placement requires 
two questions to be answered. First, where in physical space 
is it best to place controls and displays; and second, within 
that space, how should the displays and controls be 
arranged. 



Poor 



0/ 0)2 Q)3 



0)4 0)5 0)6 



4/ 


4« 


kz 


k5 


4j 


k6 



Better 



0/ 


0)2 


Oj 


0)4 


0)5 


0)6 




4/ 


42 


43 


*4 


45 


45 




Best 



Figure 6-10.— Examples of spatial compatibility between a bank 
of controls and displays. 



Arrangement of Controls and Displays 

The arrangement of controls and displays obviously in- 
volves spatial compatibility; but, beyond that, considera- 
tion must be given to grouping displays and controls with 
regard to how they are used. There are four basic principles 
for arranging controls and displays: importance principle, 
frequency-of-use principle, functional principle, and 
sequence-of-use principle. 

The importance principle states that controls and dis- 
plays that are vital to the achievement of a task be placed 
in an optimum location. The frequency-of-use principle 
states that the most frequently used controls and displays 
be given priority in a workspace. The functional principle 
provides for the grouping of controls and displays by func- 
tion, such as grouping together all controls that deal with 
the tail conveyor of a continuous miner. Finally, the 
sequence-of-use principle requires that controls and displays 
be arranged to take advantage of frequently used patterns 
or sequences of operation. 

Obviously, one cannot satisfy all of these principles at 
the same time; tradeoffs must be made. In general, the im- 
portance and frequency-of-use principles are probably most 
applicable in determining the general area in a workstation 
to locate controls and displays, while the sequence-of-use 
and functional principles apply more to the arrangement 
of components within a general area. One thing does seem 
clear, however; where there is a fixed sequence of opera- 
tion, the sequence-of-use principle should take precedence 
over the other principles. *• 

Standardization 

Transcending the preceding principles of arrangement 
is the principle of standardization. Once an acceptable 



62 



layout of components has been achieved, every effort should 
be made to standardize that arrangement within a partic- 
ular class of equipment and, where possible, across similar 
equipment. In chapter 4, a fatal accident was described that 
could be attributed to a lack of standardization between dif- 
ferent models of the same manufacturer's equipment. Lack 
of standardization probably represents the most serious and 
pervasive problem with respect to equipment design in the 
mining industry. 

Figure 6-11 shows different arrangements of roof bolter 
controls used by one manufacturer. A survey of surface min- 
ing haulage trucks and front-end loaders by Conway and 
Sanders (6) found eight different configurations for brake, 
clutch, and throttle controls on 120-st-capacity and smaller 
haulage trucks as shown in figure 6-12. In consideration 
of the many different braking systems employed, standard- 
ization of the major controls would be highly desirable, with 
recommended locations for other controls if they were 
employed. 

Figure 6-13 shows the placement of the service brake 
relative to the steering wheel in four front-end loaders found 
at surface mines (6). Again, the need for standardization 
is obvious. 

When equipment layout is not standardized, an operator 
must unlearn old habit patterns (e.g., hitting the brake with 
the left foot) and learn new patterns (e.g., hitting the brake 
with the right foot). The unlearning-learning is much more 
difficult than learning a habit pattern the first time. With 
practice, people can usually adapt; however, it is a well 
known fact that in panic or stress situations, people will 
often revert to old habit patterns or operate controls in the 
stereotypically expected manner. There are no reliable 
statistics available as to the number of accidents that were 
caused, in whole or in part, by lack of standardization in 
control-display layout. However, it was reported by White 
(33) that 72% of crane operators admitted to making control- 
input errors because of lack of standardization. 



Roof Bolter A 



1 Boom extend 

2 Canopy 

3 Fast feed 

4 Rotate 

5 Feed 

6 Drop head 

7 Stabjack 

8 Drill guide 

9 Boom swing 




Roof Bolter B 

1 Canopy 

2 Boom tilt 

3 Drill guide 

4 Drop head 

5 Feed 

6 Rotate 

7 Fast feed 

8 Stabjack 

9 Diverter 



43 |rcJ 

HE 




®— |"rs| 

S B 


© [rc| 

HE ' 



BEE 



EBB 



HE] H 





KEY 

© Steering column 

A Accelerator or throttle (floor pedal) 

B Service brake (floor pedal) 

B/B Dynamic or service brake (combination floor pedal) 

BS Rear brake (steering column mounted) 

C Clutch (floor pedal) 

RC Retarder (console mounted) 

R Retarder (floor pedal) 

RS Retarder (steering column mounted) 

TB Trailing unit brake (steering column mounted) 

Figure 6-12.— Brake, clutch, and throttle control placement on 
eight 120-st-capacity and smaller haulage trucks (adapted frorr 
6). 





Brake to the left 
of steering wheel 



Brake to the right 
of steering wheel 





Brake left or 

right of 
steering wheel 



Brake left and 

right of 

the center 



Figure 6-1 1 .—Different arrangements of roof bolter controls 
from one manufacturer (15). 



Figure 6-13.— Location of service brake relative to steering 
wheel on four front-end loaders (6). 



63 



Location of Controls and Displays 

The optimum location for controls and displays depends 
on the posture assumed by an operator in a workspace. Most 
design recommendations deal with the seated operator. 
These recommendations assume an upright seated posture 
typical of that found in computer consoles or truck vehicles. 
Rarely dealt with are semireclining work postures often 
found on low-seam mining equipment. The reclining posture 
workstations are discussed in another section of this 
chapter. 

Figure 6-14 presents a diagram showing the preferred 
vertical surface area for various classes of controls used by 
a seated operator. The dimensions are indexed from the seat 
reference point (SRP), which is at the midline of the seat 
at the intersection of the seat back and seat pan. 

Figure 6-15 presents an integrated picture of data rela- 
tive to the design of seated workstations, including fields 
of view, reach distances, and control and display place- 



ments. Placing displays and controls in these recommended 
areas helps insure that they can be seen and reached with 
minimal delay, discomfort, and errors. 

Vehicle cab design is similar to, but has important dif- 
ferences from, the typical seated console workstation. Figure 
6-16 presents recommendations for the design of vehicle 
cabs. The Society of Automotive Engineers (SAE) has pub- 
lished a recommended practice regarding the location for 
controls in heavy construction equipment (27) as shown in 
figure 6-17. This figure shows a 95th percentile male with 
the seat in the most rearward position. A 4-in forward ad- 
justment range on the seat will accommodate 90% of the 
operator population. Figure 6-17 is indexed from the H-point 
of the seat. The H-point is determined by using an anthro- 
pometric, weighted device developed by SAE. Because most 
people in the mining industry do not have access to H-point 
data about truck seats, one can approximate the location 
of the seat reference in figure 6-17 as 4.0 in to the rear and 
2.2 in lower than the H-point. 



42 



5 36 

Q_ 

UJ 
(J 



UJ 
(Z 
UJ 

u. 

Ul 

rr 
ui 

C/> 
Ul 

> 

o 

GO 

< 

Ul 

o 



CO 

o 



30 



24 



18 



12 



Maximum flat surface area for secondary controls 




1 



-24 -18 -12 -6 6 12 18 24 

DISTANCE TO RIGHT AND LEFT OF SEAT REFERENCE POINT, in 

Figure 6-14.— Preferred vertical surface areas and limits for various types of control functions operated by a seated operator (adapted 

from 20). (Courtesy of McGraw-Hill) 



64 



15° optimum eye rotation 
35° max eye rotation 
color limit 
"ST 




Standard 
line of sight ~0 e 



13 in min display distance, 
20 in preferred 



r visual limits, keep 
above to avoid glare 



Lower visual limit 



~~|~~ 5*15 

Optimum control zone 
between elbow and 



shoulder height 

6in_p 
min | 



1 




eye rotation 

Min to avoid seeing top, 54 in 

Standard horizontal 

line of sight- 0° 
Optional eye rotation 
Normal sight line, 15° 



Note, 5th-95th percentile 
operators 



Adjust 
8-IOin 



Adjust 
15-18 in 



—15 in max* 
-—26 in min 






— 24 in min ~^ 

KEY 

A Typing typewriter keyboard lowest level should be 26 in, 

upper row no higher than 31 in 
B Display -control 
C Display, setup control 
D Emergency display, setup control 
E Reference display adjust control 

Figure 6-15. — Recommended dimensions and layout of seated operator workstations (32). (Copyright 1972 by John wiiey and Sons Ltd . and 

reprinted by permission.) 



65 



8 in min Wheel diam 15-18 in 
\ Rim diam 0.75 - 1.5 in 



30 in 




25 in mm 

elbow 18-21 in 
clearance 



W l/l WW fill 



Footrest same angle as 
normal accelerating position 

n* 2by3in min clutch 

HqZE- 2 in 
S-Tin l—^g ^rake 

\ Min 10 lb, max 201b 
2 by 9 in min 



28 in max 

— to prime 

displays 



Desired up vision 




to windshield 
Standard horizontal 
line of sight 



Desired down vision, or 
so driver can see 10 ft 
60° in front of vehicle 



4 in max travel 
normal accelerator 
10° operating position 



28° min rest 



4 in min in 

Hn increments 



8 in optimum. 
4- 5 in max 10 in max 



( Note: 5th - 95th 
percentile operators) 



Figure 6-16. — Recommended Configurations Of a Vehicle cab (32). (Copyright 1972 by John Wiley and Sons Ltd., and reprinted by permission) 



66 



48 
c 40 



,_- 32 



16 

8 



8 

16 
24 



O 

u_ 

UJ 

o 

GO 

Q 



L-" 




r-fi | i | l | 1 I l 


/\ 


^ Maximum \ 


- / 


^ \ Optimum \ 


- 




^ A— — ^S^^oof Maximum 


- 




y.u "Kx^orbptimumV / - 










— 




A\^^<rl \ 1 /f^\f 




— \ \ / /v\v — 


~ , 1 . 


,1.1,1,1,1." 



40 
32 

J 24 

5 | '6 
o a: 
rx w e 

"-& 
Su. o 

2 O 
?W 8 

<n ? 

LU 
h- 
Z 24 
UJ 

o 

321 



8 8 16 24 32 40 48 
DISTANCE FROM H POINT, in 



i I ' I i 
H point pivot line 



401— i_l_i 




Hand area illustrated 
is on a horizontal 
plane 9 in above H point 



16 8 8 16 24 32 40 48 
DISTANCE FROM H POINT 

PIVOT LINE, in 



Figure 6-17.— SAE J898a recommended practice for control locations for construction and industrial equipment design (27). (Copyngm 

1974 by Society of Automotive Engineers Inc., and reprinted with permission) 



With respect to standing workstations, figure 6-18 
presents recommendations regarding placement of controls 
and displays. 

One final consideration in the placement of controls is 
the distance between them; if they are too close together, 
the wrong control is more likely to be activated. This is 
especially true when operators are wearing gloves or work- 
boots. If two controls must be operated simultaneously or 
in rapid succession, too great a distance would slow perfor- 
mance and even make it impossible to perform a task as 
intended. Figure 6-19, based on work by Chapanis (5), 
presents recommended control separations based on the type 
of control, whether one or two hands (or feet in the case of 
pedals) are being used, and whether the controls are oper- 
ated in a random sequence, sequentially, or simultaneously. 
The empty cells indicate combinations for which no reliable 
data exist. Extra space should be added between controls 
when operators wear gloves or boots (in the case of pedals). 

Special Problems in Equipment Design 

Four special problems in equipment design, especially 
relevant to the mining industry, are discussed in the follow- 
ing sections. The problems are seating for low-seam coal 
equipment, operator field of vision, egress-ingress on equip- 
ment, and access for maintenance and service. 

Seating for Low-Seam Coal Equipment Operators 

Judeikis (27) reported that of 350 underground coal mine 
fatalities involving mobile face equipment, 24 (averaging 
three per year) involved inadequate compartment size, 20 



(2.5 per year) involved an operator leaning out of the cab. 
19 (2.4 per year) involved not having an operator compart- 
ment, and 13 (1.6 per year) involved poorly designed seats. 
This represents a total of 76 fatalities related to improperly 
designed operator compartments. 

A major constraint in operator compartment design is 
the operating height of many coal mines in the United 
States. Many seams are less than 48 in high, and mine 
heights are usually no higher than the seam height. As 
pointed out by Aljoe (2), however, the practical working 
height of a coal mine is considerably less than the mine 
height because of overhead obstructions (e.g.. a roof sup- 
port timber) and undulating floor conditions. The upshot 
of this is that the height of an operator compartment may 
be as little as 22 in, thus requiring the operator to assume 
a reclined seating posture. Figure 6-20 shows three ex- 
amples of typical seating accommodations in low-seam min- 
ing equipment. 

Figure 6-21 shows diagrams of the 95th percentile male 
and 5th percentile female seating envelopes for two cab 
heights: 42 and 22 in (4). These diagrams dramatically il- 
lustrate the increased cab lengths, reduced reach envelope, 
and restricted fields of vision resulting from a reclined 
seating posture. 

Figure 6-22 presents data on the interior cab length re- 
quired for various interior cab heights to accommodate var- 
ious sizes of operators. The data assume a 10 c seat pitch 
and a 2-in helmet clearance space. As pointed out by 
Cooksey (7), the data in figure 6-22 do not take into consid- 
eration the space for a headrest or the additional cab length 
needed to depress foot pedals. 



67 



Keep lights above 
to avoid glare 



78 in maximum 
overhead control 



-IX 



VVV\VUVUV\ 



75 in 
minimum 




-r 7f k~— Standard door 
— Reference displays 

6ft£— Highest shelf 
J— Emergency display 



imum 
yiew 
30° 



Optimum 
control 



-4fV 



-20 in 
minimum 



Increase to 45 in 

to operate controls 

below 36 in 




4in 



3± 



in 



5ft v — 61 in continuous visual monitoring 
'Sr-To see over console- phone 
y\ mouthpiece 
\ Setup controls 
Display control 
—Standard wall switch 

45 in maximum for keyboard 
<T\ (angle 0°- 15°) 
1 41 in writing counter, minimum 16 in 
deep (horizontal only) 
Hand rails 
38 in door knob 
36 in standard workbench, 
minimum 24 in deep 




i ft. 



— Maintenance controls, storage 
Note, 5 th - 95 m percentile operator 



/ 



Figure 6-18. — Recommended layout Of a Standing operator workstation (32). (Copyright 1972 by John Wiley and Sons Ltd., and reprinted with permission) 



Number of body 

members and 
+-type of use 


Knobs 


Push buttons 


Toggle switches 


Cranks, levers 


Pedals 


Cdjs^_P# 


c$ 










Qfl 


I, randomly 


in 


20) 


2(l/ 2 ) 


2(3/4) 


4(2) 


6(4) 


I, sequentially 


in 




I 0/4) 


l('/ 2 ) 




4(2) 


2, simultane- 
ously 


in 


5(3) 






5(3) 




2, randomly, 
sequentially 


in 




V 2 0/ 2 ) 


3 / 4 ( 5 / 8 ) 







Figure 6-19.— Recommended separation between adjacent controls for one- and two-hand (or foot in the case of pedals) opera- 
tion, randomly, sequentially, or simultaneously. Minimum separations are given in parentheses, alongside preferred separations. 

(Adapted by McCormick and Sanders (20) from reference 5, courtesy of McGraw-Hill) 



68 






Figure 6-20.— Examples of typical seating postures in low-seam coal mining equipment. 



69 




4 8 12 16 20 24 28 32 36 40 44 48 52 56 4 8 12 16 20 24 28 32 36 40 44 48 52 56 



CAB DEPTH, in 




4 8/16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 

CAB DEPTH, in 



A 


Ankle point 


K 


B 


Knee point 


L 


C 


Hip point 


M 


D 


Shoulder point 


N 


E 


Shoulder extended 


P 


F 


Elbow point 


Q 



Standard ling of sight 
Upper line of sight 
Lower line of sight 
Warning display vision 
Controls and display vision 
Peripheral vision 



R Maximum control reach 
S Maximum control grip 
T Maximum control grip 
Z Minimum display distance 
SRP Seat reference point 



Figure 6-21 .—Seating space envelopes for 95th percentile male and 5th percentile female operators in 42-in (top) and 22-in (bottom) 

Cab heights (4). (Courtesy of Canyon Research Group Inc.) 



70 



45 



15 




w^ 50 ** 



/ 95 pet 



40 



50 60 70 

INTERIOR CAB LENGTH, in 



80 



Figure 6-22.— Relationship between interior cab height and re- 
quired interior cab length needed to accommodate various sized 
people. Assumes a 10° seam pitch and 2-in helmet clearance (7). 

(Courtesy of R. Cooksey, University of New England) 



In an effort to reduce problems common to low-seam 
operator compartments, the Bureau sponsored a research 
project to develop a human-factored, state-of-the-art, low- 
seam seat (13). Although the aim was to develop a seat for 
the remote control of mining equipment, the design could 
conceivably be adopted to on- vehicle operator compartments 
as well. Figure 6-23 shows the seat and a schematic design. 
The seat is easily adjustable and fits a wide range of opera- 
tor body sizes. The seat surface is made of strips of woven 
monofilament, open-mesh, polyester belting for strength, 
durability, and comfort. The headrest is constructed of a 
piece of standard seven-ply, neoprene conveyor belting 
looped so the bias provides maximum flexing resistance in 
the longitudinal direction. 

Operator Field of Vision 

Restricted field of vision from both surface and under- 
ground equipment is a common problem in mining. Con- 
way and Sanders (6) pointed out that restricted vision from 
operators' compartments was a serious problem for haulage 
trucks, front-end loaders, and dozers in surface operations. 
A review of the literature, however, finds that almost all 
the research and development effort has been directed 



** rf^ '^--//-Headrest 

.Backrest angle adjustment knob 




Figure 6-23.— Human-factored seat for lOW-Seam mining equipment (13). (Copyright 1 982 by the Human Factors Society Inc.. and reproduced by permission) 



71 



toward haulage truck visibility problems. MSHA deter- 
mined that lack of "visibility" was a contributing factor in 
approximately 20% of fatal and nonfatal truck haulage 
accidents during the years 1972 to 1975 (21). Poor or 
restricted field of vision greatly contributed to operators 
driving off haulage roads and over embankments, colliding 
with other equipment and fixed objects, and running or 
backing over individuals. 

To illustrate the magnitude of the field of view problem 
for haulage truck operators, figure 6-24 shows front- and 
side-vision limitations for a 150-st-capacity rear-dump 
haulage truck. As can be seen, an operator cannot see a 6-ft 
person standing closer than 40 ft in front of the truck and 
can only see the ground beyond 62 ft in front of the truck. 
Figure 6-25 presents a plan view of the same truck and 
shows the blind spots and the distances required to see an 
8-ft object and the ground around the operator's cab. 

Visibility plots such as those presented in figures 6-24 
and 6-25 are good for illustrating field of vision problems, 
but should not be considered as a totally accurate depiction 
of an operator's visual field. A single plot does not take }nto 
account different sized operators (and hence, eye heights); 




105 ft 



-Grade visibility 
line 



70 ft 
1-6- 



ft visibility line 



ft 10 ft 16 ft 
6"ft visibility line- 1 I 
Grade visibility line-' 



different seat adjustment positions and heights; and equip- 
ment modifications, such as new components on the right- 
side deck, shields over the engine, different tire sizes, etc. 
All of these factors will change the shape and size of blind 
spots. For example, a 3-in-diameter corner post in a cab 
located 33 in from an operator's eyes will block an object 
5.5 ft wide at a distance of 60 ft. 

The Bureau sponsored research to develop improved 
"visibility" systems for large haulage vehicles (14). The final 
system consisted of fresnel lens, blind area viewers; a quick- 
change left mirror; a rectangular convex right mirror; and 
a ruggedized, closed-circuit television system (16). Figure 
6-26 shows a typical system on a haulage truck. The fresnel 
lens allows an operator to see objects as close as 5 ft to the 
truck, as shown in figure 6-27. Figure 6-28 shows the im- 
proved field of visibility using the new system of lenses, mir- 
rors, and cameras. The improved system eliminated approx- 
imately 85% of the forward and right blind area, and about 
95% of the rear blind area. 

In the underground mining environment, MSHA attrib- 
uted 25 fatalities involving mobile face equipment from 
1972 through 1979 to inadequate "visibility" from the 
operator's cab (17). This represents an average of 4.6 
fatalities per year as a result of restricted field of vision. 
A system for assessing the visibility requirements for op- 
erating continuous miners, shuttle cars, and scoops was 
developed by Sanders and Kelley (25). They also developed 
a methodology for measuring the adequacy of the actual 
fields of vision for underground equipment. This method- 
ology involved a task analytic approach for identifying the 
important visual features needed to efficiently and safely 




62 ft 40 ft ft 

| L 6"ft visibility line 

'-Grade visibility line 

Figure 6-24.— Illustration of front and side visual limitations 
from the cab of a 150-st-capacity rear-dump haulage truck (27). 

(Courtesy of U.S. Mine Safety and Health Administration) 




□ Totally visible to operator 
H Viewing area 



1—1 

KEY 

E2)Blind area until 8-ft object is visible 
@ Blind area until ground is visible 



Figure 6-25.— Plan view illustrating front and side visual limita- 
tions and blind areas from the cab of a 150-st-capacity rear-dump 

haulage truck (21). (Courtesy of U.S. Mine Safety and Health Administration) 



Blind area viewers 



TV monitor 



Left rearyiew 
mirror 



Right rearvlew 
curved mirror 




Closed circuit 
TV camera 



Figure 6-26.— Typical installation of an improved visibility 
system for large haulage trucks (16). 



72 




Figure 6-27.— Fresnel lens blind area viewer used to enhance 
visual field of haulage truck operators. A person standing a few 
feet from the truck can be seen through the lens. 




Figure 6-28.— Improved field of view resulting from installa- 
tion of system shown in figure 6-27 (76). 



operate the equipment. These visual features were trans- 
lated into visual attention locations (VAL's) that should be 
visible from an operator's cab. Figure 6-29 shows a plot of 
the VAL's for continuous miner operations. (At each VAL, 
several heights above the floor should be visible.) 

The method of assessing a field of vision involved the 
use of a human eye reference measurement instrument 
(HERMI) shown in figure 6-30. By placing the instrument 
in an operator's cab and taking pictures of the cab from each 
VAL, one can easily determine if a VAL is visible from the 
cab, and if not visible, what is obstructing the view. 



Machine centerline - 
Widest machine point •» 



Necessary stopping 
distance 



*- U-Operator centerline 

—Widest machine point 




Figure 6-29.— Plan view of visual attention locations (VAL's) 
identified for continuous miner operators. Several vertical heights 
are represented at each VAL (25). 



A sample of center- and end-driven shuttle cars for high- 
and low-seam height applications, with canopies in both 
high and low positions, was evaluated by Sanders and 
Krohn (26) using these techniques. It was found that with 
a canopy in the low position, the field of vision was increased 
by placing the cab in the front of the car as opposed to the 
center or rear of the car. It was also found that adding a 
canopy did not reduce the field per se, as long as it did not 
force operators to lower their eye position. The field of vi- 
sion was degraded when the eye position was lowered, with 
or without a canopy in place. 

Across all configurations and canopy positions, six 
VAL's were not visible from any machine tested. These 
VAL's were located at floor level, on the opposite side of 
the machine from the operator's cab. and from 2 ft to the 
necessary stopping distance in front of the machine's direc- 
tion of travel. This area, then, represents a blind area on 
virtually all shuttle cars. It was recommended that mirror 
systems be developed and retrofitted on current shuttle cars 
to eliminate such blind spots. 

Egress-Ingress on Surface Mining Equipment 

Slips and falls while ascending and descending equip- 
ment account for over one-third of all surface mining lost- 
time accidents associated with the operation of haulage 
trucks, front-end loaders, track dozers, shovels, and drag- 
lines (18). A review of MSHA accident data by Gavan (10) 
revealed that almost 2.000 slip and fall accidents occurred 
on surface mine mobile equipment during 1978 and 1979 
alone. These accidents averaged 15.3 lost days per incident. 



73 




Figure 6-30.— Human eye reference measurement instrument (HERMI) used to assess fields of visibility from operators' cabs. 
The white arcs represent the 95th percentile male and 5th percentile female eye positions allowing reasonable head and trunk flex- 
ion (26). 



Characteristic injuries are cuts, lacerations, contusions, 
fractures, sprains, and strains. 

The types of generic design problems that contribute to 
the frequency of slip and fall accidents, according to Long 
(18), include 

1. Excessively flexible lower section supports for lower 
steps or rungs on ladders (fig. 6-31). 

2. Inappropriate distances from ground level to first step 
(fig. 6-32). 

3. Use of access paths that are not intended for that pur- 
pose such as the tracks on dozers and shovels. 

Added to these problems are the tendencies for mud, 
snow, ice, and oil to accumulate on the step surfaces, and 
the tendency of the operators to carry personal items with 
them, making it difficult for them to use both their hands 
to hold the rails when mounting or dismounting. 

Figure 6-33 shows recommended design guidelines for 
stairs and ladders that are applicable to surface mining 
equipment egress-ingress systems. Figure 6-34 shows two 
innovative stair designs for haulage trucks. In both cases, 
stairs replaced conventional vertical ladders for easier and 
safer egress and ingress. The pulldown stair design (figure 
6-34, top) also has the safety feature that when the stairs 



are down, the counterweight is clearly visible to the driver. 
This reduces the chance of moving a truck when someone 
is attempting to board. 

In addition to stair and ladder design, Bottoms (3) 
pointed out the need to consider the design and placement 
of the doorways for egress and ingress. Figure 6-35 shows 
a typical access path for entering a tractor. The door is 
aligned with the steering wheel, thus requiring the operator 
to maneuver around the wheel into the seat. Ideally, the 
gap between the seat and steering wheel should be opposite 
the doorway, as shown in figure 6-36. If this cannot be done, 
the effective platform width (W in figure 6-35) should be 
made as large as possible. Bottoms (3) also recommended 
door widths of 26 in at or above waist level, and 16 to 26 
in at foot level. The minimum size recommended is 22 in 
at and above waist level, and 12 in at foot level. 

The Bureau sponsored a research and development proj- 
ect to improve egress-ingress systems for surface mining 
equipment, as discussed by Long (19). Figure 6-37 shows 
the spring-supported lower step concept for large haulage 
trucks. This design consists of a lower first step that will 
flex and withstand collisions, as shown in figure 6-38, and 
still provide a semirigid mounting surface. 



74 





Figure 6-31.— Excessively flexible lower section support on 
haulage truck ladder, a common problem (18). 



Figure 6-32.— Inappropriate height of first step on haulage 
truck ladder (18). 



75 



In. 



Min 



Max 



A. 


Angle of rise: 


50° 


75° 


B. 


Tread depth : 








For 50° rise : 


6 


10 




For 75° rise: 


3 


6 


C. 


Riser height: 


7 


12 


D. 


Height .step to landing: 


6 


12 


E. 


Width, handrail-handrail: 


21 


24 


F. 


Min overhead clearance: 


5.5ft 




G. 


Height of handrail: 


34 


37 


H. 


Diam of handrail: 


I.I 


2 


I 


Min hand clearance: 


3 






In. 



Min 



Max 



A. 


Angle of rise: 


75° 


90° 


B. 


Rung or cleat diam: 








Wood: 


1.1 


1.6 




Protected metal: 


0.8 


1.6 




Metal that may rust: 


1 


1.6 


C. 


Rung spacing: 


9 




D. 


Height, rung to landing : 


6 




E. 


Width between stringers: 


12 




F. 


Climbing clearance width: 


24 




G. 


Min clearance depth: 








In back of ladder: 


6 






On climbing side. 


36 for 75° 


30 for 90° 


H. 


Height of string above landing: 


33 




I 


Max height of climb: 




10ft 




Figure 6-33.— Design recommendations for stairs and ladders, in inches (30). (Courtesy of us. Army Missile Command) 



76 





Figure 6-34.— Stairs used on haulage trucks instead of vertical ladders (6). Top, counterbalanced pulldown design; bottom, fixed 
immovable design. 



77 




Access path 



Figure 6-35.— Schematic diagram showing relationship of seat, 
steering wheel, and doorway on a typical tractor (W is effective 
platform width) (3). This design requires the driver to maneuver 

around the Steering Wheel. (Courtesy of Butterworth Scientific Ltd.) 




Figure 6-36.— Example of a well-designed access door. The 
door is aligned with the gap between the seat and the steering 
wheel rather than being offset. 



Rigid ladder 
assembly 



High-grip step 
material (typical) 




Pretension spring 
assembly (typical) 




Figure 6-37.— Concept of Bureau-sponsored four-spring- 
supported lower steps for large haulage trucks (18). 



Figure 6-38.— Bureau-sponsored four-spring-supported lower 
steps colliding with a large rock (18). 



The Bureau also supported a research and development 
project to build a hydraulic lift "power" step for access to 
an operator's cab. Its principal application is for track dozers 
and shovels. Figure 6-39 shows a man and some materials 
being transported via the power step. Both the spring- 
supported steps and the power step have been field tested 
with favorable results in terms of safety and reliability. 

Designing for Maintainability 

As mining equipment becomes larger and more complex, 
increased demands are placed on the maintenance function. 
Equipment must be routinely serviced to keep it in good 
working condition and to reduce downtime. When equip- 
ment fails, it must be fixed quickly and returned to service. 
Unfortunately, equipment is not often designed for service- 
ability or maintainability. Design problems with off- 
highway equipment were discussed by Puffer (23) and 
include poorly designed fluid level indicators that are so 
difficult to read that they are ignored, filters that are so 
difficult to reach and remove that they frequently are not 
serviced on schedule, and filler caps that are located where 
dust will accumulate and contaminate the system. 

Complex maintenance procedures are required to fix 
simple problems. On one 120-st-capacity e ] ectric drive rear- 
dump truck, for example, to remove the wheel motor, it is 
necessary to remove the truck bed, the entire rear axle 
assembly, and the casing around the axle-wheel to expose 
the motor. In another truck, to change four belts or certain 
hoses, either the radiator or the engine block have to be 
removed (18). Long also listed the following design problems 
related to haulage truck maintenance. (These problems, 
however, are not restricted to trucks, but are found with 
most mining equipment.) 

1. Poor access to machine parts or areas of the unit for 
routine or unscheduled maintenance tasks. 

2. Inadequate access openings to permit a person to reach 
or climb in to repair or replace parts. 

3. Need to remove or dismantle ancillary components in 
order to gain access to the failed unit. 



78 



****** riifm 



«L tORPORATiON 





Figure 6-39.— Bureau-sponsored hydraulic "power" step for egress and ingress from tractors, dozers, and shovels (18). 



4. Inadequate or no provisions for the safe handling of 
heavy or large parts. 

5. Inadequate tools to perform the required maintenance 
tasks. 

Often, if maintenance tasks were thoroughly analyzed 
in the initial design stage, many of the problems would be 
obvious and correctable. Unfortunately, maintenance pro- 
cedures are often not even developed until after the equip- 
ment is designed and fabricated. 

This chaper does not cover the intricacies related to 
designing for maintainability, such as designing fasteners 
and connectors; covers, cases, and shields; or cables and 
hoses. However, because inadequate access for removal and 
replacement of parts and making periodic adjustments 
ranks as one of the most prevalent maintenance design pro- 
blems, information is supplied on access space. Appendix 
E contains information regarding required work area 
clearances needed to accommodate various working 
postures, selected clearances for arms and hands, access 
spaces required to operate typical handtools, and access 
spaces required to grasp various sized objects with one or 
two hands (30). 



HANDTOOL DESIGN 

In 1983, MSHA accident data revealed 1% to 10<* of all 
nonfatal, lost-days accidents in the mining industry were 
related to handtools (31). The problem can often be traced 
to using the wrong tool for the task at hand. This is not 
surprising when one considers the vast array of specialized 
tools available. For example, Williams (34) described 25 dif- 
ferent types of wrenches for various tasks. One can hardly 
expect every maintenance person to carry a full complement 
of such wrenches in addition to all the various types of ham- 
mers, screwdrivers, etc., that are available. The result is 
that one wTench often serves multiple purposes, including 
acting as a hammer. 

In the mining industry, as in most other industries, non- 
powered handtools make up the bulk of handtool-related 
injuries, often 75°t or more. The most commonly implicated 
tools are hammers, wrenches, and knives. There is a body 
of human factors literature related to the design of hand 
tools that provides guidance with respect to size and weight, 
handle design, and positioning of trigger switches. The in- 
terested reader is referred to references 8 and 9. 



79 



Principles of Handtool Design 

This section discusses some general principles of hand- 
tool design as given by McCormick and Sanders (20). It also 
discusses the special problem posed by vibrating handtools 
such as rock drills, pneumatic chipping tools, and chain 
saws. 




Maintain a Straight Wrist 

The flexor tendons of the fingers pass through a tunnel 
in the wrist and attach to the muscles in the forearm. This 
tunnel is called the carpal tunnel because it is formed by 
the transverse carpal ligament. When the wrist is bent, the 
tendons bend and bunch up in the carpal tunnel. Repetitive 
wrist bending, or the exertion of forces by the hand with 
the wrist bent, can cause an inflammation of the tendon 
sheaths of the wrist (tenosynovitis). In addition, the median 
nerve also passes through the carpal tunnel and can be in- 
jured by the same kinds of actions that cause tenosynovitis. 
Injury to the median nerve is called carpal tunnel syndrome 
and sometimes requires surgery to correct the problem and 
relieve the pain. A common type of hand motion that can 
lead to tenosynovitis is that of "clothes wringing" (28), in 
which the wringing is done by a clockwise movement of the 
right hand and counterclockwise action of the left. This type 
of motion is involved when inserting screws in holes, and 
looping wire while using pliers. In general it is better to 
bend the tool than the wrist. Figure 6-40 shows examples 
of tools that have been redesigned to permit straight- wrist 
use. 

Avoid Tissue Compression Stress 

Often in the operation of a handtool, considerable forc< 
is applied to the palm of the hand. Handles of pliers dig in 
to the palm area; the palm is used to exert force on the top 
of a screw driver; or the palm is used to pound a wrench. 
All of these actions can damage unprotected blood vessels 
and nerves in the hand. 

Avoid Repetitive Finger Action 

Excessive use of the index finger to operate triggers can 
result in "trigger finger," where the person can flex the 
finger but cannot extend it. In general, frequent use of the 
index finger should be avoided, and thumb-operated con- 
tacts should be used. 

Design for Safe Operation 

This includes the elimination of pinching hazards, sharp 
corners, and edges; installation of braking devices in power 
tools to stop the tool quickly when the trigger is released; 
and the proper placement of on-off switches to reduce ac- 
cidental activation and permit quick response times to turn 
off the device. 

Women and Left-Handers 

The number of women in the mining industry workforce 
is increasing. The major problem women have with hand- 




']/\^/\sW/\A/\AAAA<WAA>*<WWAM>\^^ 





Figure 6-40.— Examples of common handtools designed to per- 
mit users to maintain straight wrists. 



tools is that their hands are too small to effectively operate 
some tools, such as wire strippers, crimping tools, pliers, 
and shears. The maximum grip strength can be applied 
when the handle opening of a tool is 2.5 to 3.5 in; this ap- 
plies to both males and females. The maximum handle open- 
ing should not exceed 4.0 in in order to accommodate 
smaller female hands. 

Left-handers make up about 8% to 10% of the popula- 
tion. Tools should be designed so that they can be used by 
either left- or right-handed operators. Trigger positions and 
stabilizing handles should be mounted to allow operation 
with either hand. 

Although it is often not possible for companies to design 
and fabricate their own handtools, awareness of the basic 
human factors principles can be valuable in selecting the 
proper tools for a job and for training workers in the proper 
use of handtools. 

Vibration-Induced White Finger 

The National Institute for Occupational Safety and 
Health (NIOSH) estimated that over 100,000 workers in the 
mining industry are potentially exposed to hand-arm vibra- 
tion from pneumatic and motor driven tools (22). It is now 
recognized that exposure to this sort of vibration can cause 
a condition known as vibration-induced white finger (VWF). 
Early stages of this syndrome are characterized by tingling 



80 



or numbness in the fingers. As NIOSH points out, tem- 
porary tingling or numbness during or soon after use of a 
vibrating handtool is not considered VWF. The symptoms 
must be more persistent and occur without provocation. 
Other symptoms include blanching, pain, and flushing of 
the fingers. These symptoms usually appear suddenly, and 
are precipitated by exposure to cold. With continued ex- 
posure to vibration, the signs and symptoms become more 
severe and the pathology may become irreversible. 

The recognition of VWF among miners dates back to 
the early 1900's when Hamilton (12) described spastic 
anemia of the hands among limestone quarry workers us- 
ing pneumatic chipping hammers and drills. Studies by 
NIOSH (22) found an incidence of VWF symptoms as high 
as 83% in workers exposed to vibrating handtools in 
foundries. 

Despite considerable research, little is known about the 
physiological basis of VWF or which specific vibration 
parameters are most necessary to control. It is certain, 
however, that progressive stages of VFW arise from the 
cumulative effect of trauma to the hands from regular, pro- 
longed use of vibrating handtools. 

Redesign of a rock drill and air leg unit, and reducing 
the level of vibration significantly, was reported by Rogers, 
Eglin, and Hart (24). They were not successful in their 
search for a glove material that would reduce the vibrations 
transmitted to the hand. Attempts by manufacturers to 
reduce vibration from chain saws has been very successful 
and has contributed to a reduction of VWF cases among 
chain-saw operators (2). 



DISCUSSION 

This chapter has briefly reviewed major human factors 
issues in the design of hardware and has presented some 
data, both in the chapter and in appendixes, that can be 
used to evaluate and enhance the design of mining equip- 
ment. More extensive data can be found in references 8, 30, 
32, and 35. 

The design of equipment is the culmination of a 
systematic approach that should detail the task re- 
quirements for the operator and maintainer, and incor- 
porate considerations of human limitations into the final 
design. A well-designed piece of equipment will result in 
reduced training time, higher productivity, fewer accidents, 
and greater worker satisfaction and comfort. 



REFERENCES 

1. Aljoe, W. How to Design Cabs and Canopies. Coal Min. and 
Processing, Mar. 1983, pp. 61-67. 

2. Axelsson, S. Progress in Solving the Problem of Hand Arm 
Vibration for Chain Saw Operators in Sweden, 1967 to Date. Paper 
in Proceedings of the Int. Hand Arm Vibration Conf. NIOSH, Cin- 
cinnati, OH, 1977, pp. 77-170. 

3. Bottoms, D. Design Guidelines for Operator Entry-Exit 
Systems on Mobile Equipment. Appl. Ergonomics, v. 14, 1983, pp. 
83-90. 

4. Canyon Research Group Inc. (Westlake Village, CA). Human 
Factors Design Guidelines for Personnel Carriers. 1982, 37 pp. 



5. Chapanis, A. Design of Controls. Ch. in Human Engineering 
Guide to Equipment Design, ed. by H. Van Cott and R. Kinkade. 
Wiley, 1972, pp. 345-380. 

6. Conway, E.J., and M.S. Sanders. Recommendations for Human 
Factors Research and Development Projects in Surface Mining (con- 
tract J0395080, Canyon Res. Group Inc.). BuMines OFR 211-83, 
1982, 86 pp.; NTIS PB 84-143650. 

7. Cooksey, R., G. Hartley, and A. Burks. Predictive Relation- 
ships for Cab Dimensions in Low Coal Mining Machines. Paper 
in Proceedings of the Human Factors Society 26th Annual Meeting, 
Seattle, WA, Oct. 25-29, 1982, pp. 394-399. 

8. Eastman Kodak Co. Ergonomic Design for People at Work. 
Volume I: Workplace, Equipment, and Environmental Design and 
Information Transfer. Lifetime Learning, 1983, 406 pp. 

9. Fraser, T. Ergonomic Principles in the Design of Hand Tools. 
Int. Labor Office, Geneva, Switzerland, OSHA Series No. 44, 1980, 
91pp. 

10. Gavan, G, P. Mate, D. Strassel, and K. Conway. Develop- 
ment and Demonstration of Improved Truck Ladders (contract 
H0282001, Woodward Assoc.). BuMines OFR 87-81, 1979, 335 pp.; 
NTIS PB 81-223406. 

11. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
Approach. Taylor and Francis, 1981, 379 pp. 

12. Hamilton, A. Reports of Physicians for the Bureau of Labor 
Statistics— A Study of Spastic Anemia in the Hands of Stonecut- 
ters. Sec. in Effect of the Air Hammer on the Hands of Stonecut- 
ters. Bull. 236, Industrial Accidents and Hygiene Series, No. 19, 
U.S. Dep. of Commerce, Springfield, VA, 1918, pp. 53-66, NTIS PB 
254-601. 

13. Hartley, C, R. Cooksey, and A. Kwitowski. An An- 
thropometrically Adjustable Seat for Low Seam Mining Applica- 
tions. Paper in Proceedings of the Human Factors Society 26th An- 
nual Meeting, Seattle, WA, October 25-29, 1982, pp. 389-393 

14. Hawley, K.W., and S.F. Hulbert. Improved Visibility Systems 
for Large Haulage Vehicles (contract H0262022, MB Assoc.). 
BuMines OFR 100-78, 1978, 121 pp.; NTIS PB 286-065. 

15. Helander, M., E.J. Conway, W. Elliott, and R. Curtin. Stan- 
dardization of Controls for Roof Bolter Machines. Phase I. Human 
Factors Engineering Analysis (contract H0292007, Canyon Res. 
Group Inc.). BuMines OFR 170-82, 1980, 192 pp.; NTIS PB 
83-119149. 

16. Johnson, G.A. Improved Visibility System. Paper in Surface 
Mine Truck Safety. Proceedings of Bureau of Mines Technology 
Transfer Seminars, Minneapolis, Minn., June 25. 1980; Birm- 
ingham, Ala., July 9, 1980; and Tucson, Ariz., July 24, 1980; comp. 
by Staff, Bureau of Mines. BuMines IC 8828, 1980, pp. 22-39. 

17. Judeikis, J. (MSHA, Triadelphia, WV). Personal communica- 
tion, 1980; available upon request from M.S. Sanders, Essex Corp.. 
Westlake Village, CA. 

18. Long, D.A. Solving the Problem of Getting On and Off Large 
Surface Mining Equipment. Paper in Safety in the Use and 
Maintenance of Large Mobile Surface Mining Equipment. Pro- 
ceedings: Bureau of Mines Technology Transfer Seminars, Tucson, 
AZ, August 16, 1983; Denver, CO, August 18, 1983; and St. Louis, 
MO, August 23, 1983, comp. bv Staff, Bureau of Mines. BuMines 
IC 8947, 1983, pp. 3-16. 

19. Improved Personnel Access for Surface Mining Equip- 
ment. BuMines IC 8983, 1984, 20 pp. 

20. McCormick, E., and M. Sanders. Human Factors in Engineer- 
ing and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 

21. Miller, W. Analysis of Haulage Truck Visibility Hazards at 
Metal and Nonmetal Surface Mines, 1975. MSHA IR 1038. 1976. 
19 pp. 

22. National Institute for Occupational Safety and Health. Vibra- 
tion Syndrome. NIOSH 83-110, 1983, 21 pp. 

23. Puffer, W. Designing for Reduced Repair Labor Costs. Soc. 
Automotive Eng., Warrendale. PA, SAE Tech. Pap. 81099. 1981. 
10 pp. 



81 



24. Rogers, L., D. Eglin, and W. Hart. Rock Drill Vibration and 
White Finger in Mines. Ch. in Vibration Effects on the Hand and 
Arm in Industry, ed. by A. Brammer and W. Taylor. Wiley, 1982, 
pp. 317-323. 

25. Sanders, M.S., and G.R. Kelley. Visual Attention Locations 
for Operating Continuous Miners, Shuttle Cars, and Scoops. 
Volume I (contract J0387213, Canyon Res. Group Inc.). BuMines 
OFR 29(l)-82, 1981, 142 pp.; NTIS PB 82-187964. 

26. Sanders, M.S., and G.S. Krohn. Validation and Extension 
of Visibility Requirements Analysis for Underground Mining 
Equipment (contract J0318072, Canyon Res. Group Inc.). BuMines 
OFR 154-83, 1983, 65 pp.; NTIS PB 83-252957. 

27. Society of Automotive Engineers (Warrendale, PA). Recom- 
mended Practice for Control Locations for Construction and In- 
dustrial Equipment Design. Standard J898, 1974, 3 pp. 

28. Tichauer, E. The Biomedical Basis of Ergonomics. Wiley, 
1978, 99 pp. 



29. U.S. Air Force Systems Command. Human Factors Engineer- 
ing. Aeronautical Systems Div. AFSC DH 1-3, 1980, 582 pp. 

30. U.S. Army Missile Command. Military Standardization 
Handbook: Human Factors Engineering Design for Army Material. 
MIL-HDBK-759A, 1981, 79 pp. 

31. U.S. Mine Safety and Health Administration. Mine Injuries 
and Worktime Quarterly, Jan.-Dec. 1982. 1983, 18 pp. 

32. Van Cott, H., and R. Kinkade. Human Engineering Guide 
to Equipment Design. Wiley, rev. ed., 1972, 752 pp. 

33. White, T. Ergonomic Survey of Mobile Cranes. Appl. 
Ergonomics, v. 4, 1973, pp. 96-104. 

34. Williams, J. Selection of Hand Tools Leads to Efficient, Safe 
Use. Coal Age, v. 80, 1975, pp. 108-112. 

35. Woodson, W. Human Factors Design Handbook. McGraw- 
Hill, 1981, 1049 pp. 



82 



CHAPTER 7.— PHYSICAL WORK 




Mining will always be a physically demanding occupation, but by proper design of the tasks and worksites 
and through employee training, the incidence and severity of injuries can be reduced 



Despite increased mechanization, mining remains one 
of the most physically demanding occupations in the world. 
For " .'Tiple, it was found by Van Rensburg (37) 1 that in 
£• th rican gold mines with increased mechanization, 
more people were working in less strenuous jobs, but the 
physical demands of the tasks themselves were not reduced. 
The high physical demands inherent in mining take their 
toll in injury and productivity. Underground mining labor 
is especially susceptible because of the cramped working 
conditions and the presence of heavy objects that must be 
lifted and carried. Rock dust sacks can weigh 50 lb; a 75-ft 
roll of brattice, 60 lb; and a 6- by 10-in, 14-ft wood crossbar, 
over 200 lb. With such loads, it is not suprising that back 
injuries constitute the largest single type of lost-time ac- 
cidents in the mining industry, accounting for approximate- 
ly 25% of all lost-time injuries, 5,458 in 1981 alone (30). Fur- 
ther, this type of injury accounts for more lost workdays 
than any other single type. In 1981, for example, Peay (30) 
noted that 40% of lost-time back injuries incurred by 
underground coal miners resulted in more than 4 weeks of 
lost time per individual. 

In addition to the pain and suffering caused by injury, 
physically demanding tasks take their toll on productivity 
by fatiguing the worker. The more demanding the task, the 
more rest the worker needs. 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



This chapter will review the basics of work physiology 
and manual materials handling, and the demands of com- 
mon mining tasks. Recommended limits on physically 
demanding work will be discussed, as well as human fac- 
tors methods for reducing the risks involved in such work. 



WORK PHYSIOLOGY 
Muscles 

Muscles in our bodies allow us to move and to perform 
useful work. Approximately 40% of one's total body weight 
is composed of muscle. Each muscle consists of large 
numbers of muscle fibers ranging in length from 0.2 to 5.5 
in. The diameter of an individual muscle fiber is about four 
ten-thousandths of an inch, and a muscle can have a million 
such fibers. 

The most important characteristic of muscle is its ability 
to contract; that is, it can shrink to about two-thirds of its 
normal length. Each muscle fiber contracts with a certain 
force, and the strength of the whole muscle is the sum of 
the forces produced by these muscle fibers. Hence, the cross- 
sectional area of a muscle determines its strength. A mus- 
cle produces its greatest force at the beginning of its con- 
traction when it is at its relaxed length. As a muscle 
shortens, its power declines. 



83 



Muscular contraction is initiated by an electrical im- 
pulse. This electrical activity can be detected and measured 
by a technique known as electromyography. Electrodes are 
attached (taped) to the surface of the skin over the muscle 
to be examined. The exact placement of the electrodes is 
important to insure reliable and valid data. Skin electrodes 
record the total electrical activity of the muscle. The 
readings appear as rapid pen movements on a strip chart 
recorder, much like those produced by a seismograph dur- 
ing an earthquake. These recordings can be calibrated to 
yield measurements of the force of the muscle contractions. 
Figure 7-1 shows electromyograms (EMG's) of a biceps mus- 
cle producing 15, 30, 45, and 60 ft-lb of static torque (22). 
As can be seen, the higher the torque being produced, the 
greater the electrical activity and the more "violent" the 
pen recordings. 

EMG's are usually processed electronically to yield a 
simple integrated score. The use of this method, however, 
requires well-trained technicians and precisely calibrated 
equipment. 

Energy Consumption 

To perform work a muscle must expend energy. The 
detailed process by which a muscle obtains the energy 
needed to perform work is complex and beyond the scope 
of this report. The interested reader can consult Astrand 
and Rodahl (3) or Weiser (38). For the purposes of this report, 
a somewhat simplified presentation will suffice, as given 
by Grandjean (17). 

Muscle work is accomplished by the transformation of 
chemical energy into mechanical energy. Energy is released 
in a complex series of chemical reactions. Figure 7-2 shows 
a very simplified diagram of the process. A muscle get its 



Static torque produced, ft~lb 



60 



45 



30 






Figure 7-1 .— Electromyogram recording of biceps muscle dur- 
ing Static force application (22). (Copyright 1 973 by the Human Factors Society 
Inc., and reproduced by permission) 



Without O2 



Lactic acid 




J _Paytag_off _J With I 
0, debt ^J 



KEY 

Energy flow 

Chemical reactions 

Figure 7-2.— Schematic representation of metabolic process 

that takes place during muscular work ( 1 7). (Courtesy of Taylor and Fran- 
cis Ltd.) 



energy from the breakdown of high-energy phosphate com- 
pounds into low-energy compounds; this process does not 
require oxygen. The problem is that there are not a lot of 
high-energy phosphate compounds available in a muscle, 
and they must be regenerated to provide additional energy 
for the muscle. This regeneration process requires energy 
from other chemical reactions. 

The main energy source for the regeneration process 
during intense physical work is glucose, a sugar circulating 
in the blood. Glucose is converted into pyruvic acid, and this 
liberates energy for the regeneration process. The further 
breakdown of pyruvic acid depends on whether sufficient 
oxygen is present in the system. If pyruvic acid is being pro- 
duced in small quantities, enough oxygen will be available 
to break down the acid into water and carbon dioxide 
(aerobic glycolysis). This breakdown is also a source of 
energy for the regeneration process. 

If, however, insufficient oxygen is available to break 
down pyruvic acid, then the pyruvic acid is converted into 
lactic acid, a metabolic waste product (anaerobic glycolysis). 
This conversion releases a small amount of energy that can 
also be used for the regeneration process. The build up of 
lactic acid in a muscle, however, will cause it to cease con- 
tracting. To eliminate the lactic acid, oxygen is needed to 
first convert the lactic acid back to pyruvic acid and then 
to water and carbon dioxide, thus releasing more energy 
for regeneration of the high-energy phosphate compounds. 

From this thumbnail sketch, it can be seen that at the 
outset of physical work, a muscle does not need oxygen to 
function. A sprinter, for example, can run a 100-yd dash 
without taking a breath (14). This is because energy is 
released from the breakdown of high-energy phosphate com- 
pounds and from the breakdown of glucose to pyruvic acid 
and pyruvic acid to lactic acid. At the completion of a run, 
however, the sprinter would be breathing heavily, and his 
or her heart would be pounding. The runner is said to be 
in oxygen debt. That is, the body must take in oxygen, after 
the muscular work has been completed, to convert the lac- 
tic acid back to pyruvic acid and ultimately to water and 
carbon dioxide. The energy released is used to regenerate 
the high-energy phosphate components depleted during the 
run. 

The body does not respond immediately to the onset of 
heavy work; it takes a couple of minutes until the body 
mobilizes its forces to supply the working muscles with ox- 
ygen. Figure 7-3 shows the oxygen uptake, over time, in 
response to physical work. The initial lag creates an oxygen 
deficiency that is made up during recovery, when the ox- 
ygen debt is repaid. 



Cardiac Output and Aerobic Capacity 

The body mobilizes to supply increased quantities of ox- 
ygen and glucose to the working muscle. Just breathing 
deeper and faster, however, does little to increase the ox- 
ygen supply in the blood; this because blood leaves the lungs 
97% saturated with oxygen under normal healthy condi- 
tions. The only way to increase the supply of oxygen to a 
muscle is to pump more blood through the muscle. This is 
done by increasing the heart rate (beats per minute) and 
increasing the volume of blood pumped with each beat 
(stroke volume). Combined, the overall cardiac output (liters 
of blood per minute) increases. At rest, the cardiac output 
is about 5 L/min. Coincidentally, the average adult body 
contains only about 5 L of blood. In severe work, a fourfold 



84 



2 - 



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Z> 

° I 



1 1 1 1 1 1 1 1 1 


_ Adjustment Steady state 


Recovery 


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7 ^ 


- o 2 >^~ 

deficit/^ 


X 


;/ 


Rest 

l.i.i. 


,O z debt/^ 

I , I 



6 
TIME, min 



IO 



12 



Figure 7-3.— Oxygen uptake during muscular work, showing 
oxygen deficiency at the outset of work and the repayment of 
the oxygen debt during recovery. 



to fivefold increase in cardiac output, 20 to 25 L/min, can 
take place. 

There is a limit to the capacity of the body to increase 
cardiac output and, hence, deliver oxygen to the muscles. 
This leads to an important concept: maximum aerobic 
capacity (V0 2 max). This is the maximum oxygen uptake 
(consumption) the body is capable of delivering. Individuals 
have different aerobic capacities because of such things as 
their degree of physical training, age, sex, and ability of 
their blood to carry oxygen. For discussion of how to deter- 
mine an individual's maximum aerobic capacity, see 
reference 21. The concept of maximum aerobic capacity is 
important for determining safe levels of energy expenditure 
over the course of a workday, which will be discussed later 
in this chapter. 

The aerobic work capacity of U.S. low-seam 
underground coal miners was measured by Ayoub (4-5). The 
results are shown in figure 7-4. Aerobic capacity declines 
with age (the exception in the over 50-yr group is probably 
due to the small sample of miners tested) and is lower for 
females. In comparing these results with American Health 
Association norms (1), the low-seam coal miners would be 
rated about average in terms of cardiovascular fitness. As 
shown in figure 7-4, the aerobic capacity of American low- 
seam coal miners is below the levels of physical work 
(aerobic) capacity of South African miners (28), and 
Norwegian and Romanian miners (39). American miners 
were also heavier than the other groups. 

Ayoub (4) speculates that since low-seam coal miners 
engage in tasks that require short intervals of work with 
high energy expenditures, it is possible that these miners 
become specifically trained in the anaerobic (without ox- 
ygen) energy mode. 



MEASUREMENT OF WORK 

The basic unit of energy, heat, or work is the calorie. 
A kilocalorie is equal to 1,000 cal and is the basic unit of 
energy expenditure. 2 A kilocalorie is the amount of heat 



KEY 

I I American low-seam 
coal miners 

V/A Romanian miners - 
South African miners 
Norwegian workers 




20-29 30-39 40 "49 

AGE, yr 



>50 



2 The calorie is now obsolete and has been superseded by the joule (1 cal 
= 4.2 J). Since most of the literature still uses kilocalories (1 kcal = 4.2 kJ> 
it will be used in this chapter. 



Figure 7-4.— Aerobic capacity of male miners by age group (4, 
28, 39). 



needed to raise 1 L (a little over a quart) of water, 1 °C (from 
20° to 21 °C). In dietary circles, the term "Calorie" is equal 
to 1 kcal. 

To determine the energy requirements of a given task, 
the amount of oxygen consumed by the person doing the 
task needs to be known. Based on the typical Western diet, 
it is known that for every liter of oxygen consumed, approx- 
imately 5 kcal of energy is expended. That energy is used 
by the muscles to perform work and is also given off as heat 
during the various chemical reactions discussed previously. 
Approximately 75% of the energy liberated by the body goes 
to heat; only about 25% is used for work. This le%*el of effi- 
ciency is better than a steam engine, but not quite as good 
as an internal combustion engine. 

Measuring oxygen consumption can be cumbersome, re- 
quiring the person performing the task to wear a 
mouthpiece, nose clip, and gas-measuring device on his or 
her back. Flexible hoses connect the mouthpiece to the 
measuring device. Fortunately, there is an easy way to 
estimate oxygen consumption without actually measuring 
it while performing the task. Heart rate and oxygen con- 
sumption are linearly related within the range from 
moderate to close-to-maximum work loads. 

Once the specific linear equation relating heart rate to 
oxygen consumption for an individual is known, oxygen con- 
sumption can be estimated based on heart rate measured 
while performing the task. It should be pointed out. 
however, that factors such as heat, fatigue, and smoking 
can distort the relationship between heart rate and oxygen 
consumption. 

Heart rate can be measured with a few wires attached 
to the subject and a tape recorder or telemetry device the 



85 



size of a cigarette package. The problem is that the equa- 
tion relating heart rate to oxygen consumption is not the 
same for everyone. Physical fitness is a major factor deter- 
mining individual differences. Figure 7-5 shows examples 
of heart rate-oxygen consumption relationships for various 
adult men; the steeper the slope of the line, the better the 
physical condition of the individual (20). 

Therefore, to use heart rate to predict oxygen consump- 
tion, an individual must be calibrated. This is done by hav- 
ing the person perform a task at different levels of effort 
(e.g., walking on a treadmill at different speeds), while both 
heart rate and oxygen consumption are being measured. 
From such data, the relationship can be determined. 

There are two types of muscular effort, dynamic (rhyth- 
mic or isotonic) and static (isometric). Dynamic effort is 
characterized by an alternation of contraction and relaxa- 
tion of a muscle. During dynamic effort, the alternating con- 
traction and relaxation squeezes blood through the muscle, 
thereby supplying the working muscle with glucose and 
oxygen. 

Static effort, in contrast, is characterized by a prolonged 
state of contraction of the muscles. Examples of static ef- 
fort are bending over at the waist and holding that posture 
while repairing a piece of equipment, or holding the arms 
out in front of the body while hanging brattice, as shown 
in figure 7-6. During static effort, the blood vessels are com- 
pressed by the muscle itself so that blood flow through the 
muscle is reduced or stopped. The flow of blood is constricted 
in proportion to the force exerted by the muscle. Grandjean 
(17) indicates that blood flow is almost completely inter- 
rupted if the effort is 60% of the maximum effort possible. 
At 15% to 20%, blood flow should be normal. 



_l 

LU 
XL 

< 

Q_ 

3 



CD 

>- 
X 

o 




80 120 160 200 

HEART RATE, beats /min 

Figure 7-5.— Linear relationship between heart rate and oxygen 

uptake for Six adult males (20). (Copyright 1973 by the Human Factors Society 
Inc., and reproduced by permission) 






Figure 7-6.— Underground worker hanging brattice cloth with arms at full extension and static loading of shoulder muscle. 



86 



The impaired blood flow allows waste products (prin- 
cipally lactic acid) to build up in the muscle, leading to acute 
pain and muscle fatigue. The maximum duration of a con- 
traction is related to the force exerted. Exerting a force of 
50% of maximum can be endured, at most, for 1 min. Forces 
of 25% of maximum can be maintained for about 3 to 4 min, 
while forces of 20% or less can be endured for 10 min or 
more. 

All tasks involve components of both static and dynamic 
effort. The static component, however, is by far the most 
fatiguing and should be reduced if possible. Static effort can 
be decreased by reducing the effort required, switching com- 
ponents of the task so that muscle groups can be alternately 
flexed and relaxed, and inserting numerous small rest 
breaks during the task. 



ENERGY EXPENDITURE AT WORK 

There are many factors that affect the energy expen- 
diture involved in performing a task. With respect to lift- 
ing objects, the principal ones are the following: 

1. Body weight.— A task that requires a person to move 
his or her body will require more energy the heavier the 
weight of the person's body. Tasks that involve carrying 
objects or picking up objects by squatting or bending at the 
waist are examples of those affected by body weight. 

2. Body posture.— For example, a squat lift requires more 
energy than a stoop lift (straight leg, bent at the waist), 
because more of the body must be lifted in a squat lift. 

3. Weight of objects moved.— The heavier the load to be 
moved, the greater the work performed, and hence the 
greater the energy expenditure. Figure 7-7, based'on the 
work of Brown (7), for example, shows the combined effect 
of weight of load and lifting pos'ture on energy expenditure. 

4. Work pace.— Work pace is defined as the number of 
times an activity 'is- performed per unit of time. In normal 
lifting, it is the number of lifts per minute. As shown in 
figure 7-8, it appears that the relationship between work 
pace and energy expenditure is essentially linear (18). 

5. Distance traveled— The distance a load is moved, or the 
distance over which a force is applied, is directly related 
to energy expenditure. In normal lifting, it is the vertical 
distance the load is lifted that is most important. 

6. Temperature and humidity— In general, the higher the 
temperature and humidity, the greater will be the energy 
expenditure for tasks performed in such environments. Part 
of this increase is due to a general increase in metabolic 
rate in hot environments. 

One additional factor that impacts energy expenditure, 
and is especially important in normal lifting, is the vertical 
heights of the beginning and end points of the lift. Lifting 
the same distance, but starting at different heights, may 
require the lifter to assume different body postures and may 
involve differential movement of the body's center of grav- 
ity, as illustrated by the data in table 7-1. Although the 
same overall mechanical work is being performed, the 
energy expenditure is greater for the task that starts out 
at a lower height (task B), despite the fact that the work 
pace is less. 

Figure 7-9 shows the energy efficiency (energy per unit 
mechanical work) for lifting various weights 20 in from 
various starting positions (12). The most energy efficient 
lifting occurs when the starting position is between 39 and 
59 in above floor level. When the starting position is below 
39 in the efficiency is greater the heavier the load. This is 



true because the energy required to lift the body is constant, 
no matter what the load. 

Grades of Physical Work 

Table 7-2 defines seven grades of work, including rest, 
based on energy expenditure. Also included are associated 
average heart rates and oxygen consumption values. The 
data presented apply to reasonably fit adult males. 

Energy Expenditures for Common Mining Tasks 

In a survey of low-seam coal mining tasks, Ayoub (4) 
identified the following jobs as most physically demanding: 
roof bolter, bolter helper, miner helper, and timberman. 
Table 7-3 shows the energy expenditure on these jobs and 
for the task of shoveling; the grade of work to which each 
corresponds is also shown. The energy expenditure for 
shoveling is unusually high because this task is performed 
at a rapid work pace at the coal face. In addition, it was 
reported by Morrisey (24) that the energy cost of shoveling 
increases as a worker is forced to assume a more stooped 
posture, common in low-seam mines. At 60% of a normally 



Table 7-1.— Effect of vertical starting position 
on energy expenditure (27) 

(Courtesy of National Institute for Occupational Health) 





Task 




A 


B 


Load lb . . 

Work pace lifts/min . . 

Vertical starting position in . . 

Vertical ending position in . . 

Mechanical work performed kg-m . . 

Energy expenditure kcal/min . 


10 

25 

36 

66 

86.6 

3.56 


10 
21 
'0 
36 
86.0 
677 



1 Floor. 



Table 7-2.— Grade of physical work 
based on energy expenditure level 1 (2) 

(Reprinted with permission by American Industrial Hygiene Assoc ) 





Energy expenditure, kcal 


Heart rate, 
beats/min 


Oxygen 
consumption. 




Per min 


Per 8-h day 


L/min 


Rest (sitting) 

Very light work 

Light work 

Moderate work 

Heavy work 

Very heavy work .... 
Unduly heavy work. . 


1.5 
1.6- 2.5 
2.5- 5.0 
5.0- 7.5 
7.5-10.0 
10.0-12.5 
>12.5 


720 
768-1.200 
1,200-2.400 
2.400-3,600 
3,600-4.800 
4.800-6.000 
>6.000 


60- 70 

65- 75 

75-100 

100-125 

125-150 

150-180 

>180 


0.3 
0.32- .5 
.5 -1.0 
1.0 -1.5 
1.5 -2.0 
2.0 -2.5 
>2.5 



' Assumes a reasonably fit adult male. 



Table 7-3.— Energy expenditures for four low-seam tasks (4), 
kilocalories per minute 

Task and grade of work Expenditure 

Shoveling, neavy worn 9.3 

Helping, 1 moderate work 7.2 

Timbering, moderate work 6.0 

Roof bolting, light work 4.9 

1 Includes both continuous miner and roof bolter helpers. 



87 




10 20 30 40 
LOAD, kg 

Figure 7.7— Effect of weight of objects being lifted and lift 

posture on energy expenditure (27). (Courtesy of National Institute for Oc- 
cupational Safety and Health) 



E 



o 

o 



LjJ 

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Q 
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LlI 
Q. 
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q: 
lu 

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ll.4-kg 
cartons - 




Average 



4. 5 -kg cartons 



6 8 10 12 14 16 
WORK PACE, cartons/min 

Figure 7-8.— Effect of work pace on energy expenditure for a 

lifting task (18). (Copyright 1969 by the American Institute of Industrial Engineers, 
and reprinted by permission) 



Least 
efficient 




Most 
efficient 5 10 1 5 20 

WEIGHT, kg 

Figure 7-9.— Energy efficiency of lifting various weights from different starting positions (12). (Courtesy of Butterworth Scientific Ltd.) 



88 



erect posture, for example, energy expenditure was 13% 
higher than in a fully erect posture. Table 7-4 presents 
energy expenditure data collected in South African gold 
mines on additional tasks. In handling rock dust bags (50-55 
lb each) or arch sections (12 legs, 180 lb each; 6 crowns, 170 
lb each), it was found by Sims (33) that the energy expen- 
diture was approximately the same, 6.0 kcal/min (moderate 
work). 



Table 7-4.— Average energy expenditures for mining tasks 

in South African gold mines (37), 

kilocalories per minute 

(Reprinted with permission by Chamber of Mines South Africa) 

Task and grade of work Expenditure 

Transport of explosives (25 lb), moderate work 6.85 

Shoveling, moderate work 5.85 

Mechanical loader operators, moderate work 5.20 

Barring down, light work 4.75 

Equipping: Pipes and tracks, light work 4.65 

Tip operator, light work 4.43 

Timbering, light work 4.40 

Sweeping, light work 3.95 

Pneumatic drill operator, light work 3.95 

Stonewall building, light work 3.90 

Pneumatic drill assistant, light work 3.15 

Locomotive driver, light work 2.60 

Winch driving, light work 2.55 



bolter helper. As can be seen, energy levels peak at approx- 
imately 11 kcal/min (very heavy work), but dip as low as 
5.0 kcal/min (light work) elsewhere during the cycle. 

Ayoub (4) calculated the total energy expenditure over 
a 7.5-h shift (8 h minus 0.5 h for lunch) including idle time, 
travel, and other activities for the workers they analyzed. 
The results were as follows: Helpers (moderate work), 
2,789-kcal expenditure for 7.5-h shift (average of 6.1 
kcal/min); roof bolters (light work), 2,102-kcal expenditure 
for 7.5-h shift (average of 4.7 kcal/min). 

Although several tasks in mining require high levels 
of energy expenditure over short time periods, the level of 
work is generally in the light to moderate class. This, of 
course, is because the workers intersperse rest breaks in 
the work cycle or alternate between heavy and light activ- 
ities. With the exception, perhaps, of shoveling, it appears 
that high levels of cardiovascular fitness, although desir- 
able, are not necessary to perform the majority of mining 
tasks. Thus, females who generally have lower aerobic 
capacities than men should be able to function well in 
overall mining operations. As Ayoub (4) points out, how- 
ever, females and small males may be limited because of 
strength, as opposed to aerobic, capacity in their ability to 
perform mining tasks as such tasks are performed today. 



RECOMMENDED ENERGY EXPENDITURE LEVELS 



When these values are reviewed, it must be remembered 
that changes in the work pace or the method of carrying 
out the task can significantly affect the energy expenditure 
levels. Further, the energy expenditure during performance 
of a task varies widely depending on the specific cycle of 
activity. Figure 7-10, for example, presents the energy ex- 
penditure levels during a work cycle for a low-seam roof 



The National Institute for Occupational Safety and 
Health (NIOSH) recommends that short-term energy expen- 
diture levels (for 1 h or less) should not exceed 9 kcal/min 
for physically fit males or 6.5 kcal/min for physically fit 
females (27). The difference between the male and female 
recommendations is due to the generally lower aerobic 
capacity of females. 



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P r 




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LU 

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Z> 

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14 



16 



18 



2 4 6 8 10 12 

TIME, min 

Figure 7-10.— Energy expenditure and activity profile for roof bolter helper (4). 



JO 
20 



89 



Long-term energy expenditure levels (averaged over a 
workday) should not exceed 5.0 kcal/min for males and 3.5 
kcal/min for females. These values correspond to approxi- 
mately 33% of the average aerobic capacity of males and 
females. NIOSH points out, however, that these guidelines 
do not reflect the increased metabolic costs associated with 
overweight or poorly conditioned individuals. 

Based on the aerobic capacity of males and females, and 
these NIOSH recommendations, the recommended maxi- 
mum working time for tasks requiring various levels of 
energy expenditure can be computed. Figure 7-11, for ex- 
ample, shows recommended maximum working times for 



males and females performing various low-seam mining 
tasks. This figure gives maximum times for the 5th, 50th, 
and 95th percentile males and females. The 5th percentile 
represents the bottom 5% of the population in terms of 
aerobic capacity and recommended work time. The 50th 
percentile is the average, and the 95th percentile is what 
can be expected by someone who is 5% from the top of the 
population 

Several authors have attempted to develop formulas to 
predict the amount of rest required, or the amount of work 
permitted before rest is required. Unfortunately, the for- 
mulas do not always produce the same results. 



O 
O 



LU 

rr 

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15 



10 



i — i i i i 



Task and ** 

energy expenditure 
(kcal/min) 

"Shoveling (9.28) 



KEY 

— *95th percentile 

— 50th percentile 

— — — 5 th percentile 



Timbering (6.0) 



Bolting (4.9) 




- 2 



Helping bolter or miner (7.15) 



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Task and 










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(kcal/min) 










^- Shoveling 


(9.28) 








— 


Helping bolter ^** 




or miner (7.15) 


'^^"^ 




' • _^ 


^* • 




Timbering (6.0) 




'"* •* 


•*"^*" 


" • — 


_ Bolting (4.9) 












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500 



RECOMMENDED MAXIMUM WORK TIME, min 



Figure 7-11.— Recommended maximum work times for males and females performing tasks in low-seam coal mines at various 
levels of energy expenditure (4). 



90 



One formula embraced by the American Industrial 
Hygiene Association (AIHA) (2) is based on the assumption 
that over an 8-h shift, average energy expenditures should 
not exceed 5.5 kcal/min. Because at-rest energy expenditure 
is 1.5 kcal/min, the 5.5 kcal/min figure really represents 
an actual work expenditure of 4.0 kcal/min. The following 
formula computes the needed rest allowance expressed in 
terms of percentage of time working: 



RT% = 



W- 1.5 
4.0 



1 x 100, 



where RT% = rest allowance 
and W = energy expenditure during work, 
kcal/min. 



Murrell (26) presented another formula similar to the 
AIHA formula, but which computes directly the number of 
minutes of rest required. The formula assumes a maximum 
average energy expenditure of 5 kcal/min. Murrell's for- 
mula is as follows: 



RT = 



T (W - 5) , 
(W - 1.5) 



where RT = rest time, min, 

T = work time, min, 
and W = energy expenditure during work, kcal/min. 

Application of these formulas to a male shoveling coal 
in a low-seam mine (9.3 kcal/min) for 10 min yields the 
following calculations: 



AIHA formula-RT% = 



9.3 - 1.5 
515 



1 x 100 = 95%, or 



95% of 10 min work = 9.5 min rest, and 
Murrell formula-RT = ^I'l^l) * = 5.5 min rest 



Of equal or even greater importance than the amount 
of rest is the arrangement of the rest periods. In general, 
the greater the energy cost of a task, the more frequently 
rest pauses should take place. There is less cumulative 
fatigue and less demand on the heart and lungs with many 
short rests (every 0.5 to 2 min) than with the same amount 
of total rest time taken in fewer, but longer breaks. In ad- 
dition, hot environments make extra demands on the cir- 
culatory system, and hence the rest requirements are 
greater than in cool environments. 

Muller (25) presented a formula that attempts to predict 
when to take a rest. Muller assumed that people have a 
25-kcal energy reserve that is only tapped when work ex- 
ceeds 5 kcal/min. His formula is based on taking a rest when 
the 25-kcal reserve is used up. He further assumed that at 
rest, the reserve is rebuilt at the rate of 3.5 kcal/min (5 
kcal/min - 1.5 kcal basal metabolic rate). Hence, all rests 
are 7 min long (i.e., 25/3.5). The formula is as follows: 



WT = 



25 



(W-5) 



where WT — work time, before rest is required, 

and W = energy expenditure during work, kcal/min. 



Application of this formula to a 9.3-kcal shoveling task 
yields 



WT = 



25 



(9.3 - 5) 



= 5.8 min. 



That is, after 5.8 min of work, a shoveler should rest for 
7 min. For 10 min of work, he or she would require 1.7 rests 
(10/5.8) of 7 min each for a rest total of 12 min. This can 
be compared to the 9.5-min and 5.5-min values obtained by 
applying the AIHA and Murrell's formulas, respectively. 
Unfortunately, there are no objective data available to 
determine which formula should be used to determine the 
amount of rest required. The fact that most mining tasks 
are self-paced, compensates in part for the heavy work loads. 
However, workers cannot always be depended upon to take 
rest breaks at the best times. Work-rest cycles can be em- 
pirically determined by testing various combinations and 
monitoring heart rate and oxygen consumption during the 
work and rest phases. A good work-rest schedule should 
result in significant recovery of heart rate during the rest 
period and little increase in oxygen consumption during suc- 
cessive work periods. One known fact is that people are poor 
judges of when they require rest. Usually, by the time a 
person feels tired, an inordinately long rest will be required 
for recovery. A rest break should be taken before the need 
for one is felt. 



MANUAL MATERIALS HANDLING 

Materials handling involves the lifting, pushing, pull- 
ing, or shoveling of materials or components used during 
equipment or mine maintenance activities. Generally 
speaking, there is more manual handling of materials in 
underground mining than in surface mining. This is due 
to several factors, including a greater variety of supplies 
used and the difficulty of using mechanical handling devices 
underground. Unger and Connelly (35) cataloged materials 
handling activities in underground mining into five 
functions: 

1. Production supply.— Handling materials from the sur- 
face yard to locations near the working face. Examples 
would include transporting rock dust bags, roof bolts, and 
timbers. 

2. Production end use.— Handling items during their end 
use at the working face. Such work activities would include 
erecting temporary curtains for ventilation, rock dusting, 
roof bolting, and erecting cribbings. 

3. Section move.— Handling materials from the surface 
yard to the section being moved, including the handling dur- 
ing the process of moving a mining section. Examples in- 
clude moving haulage belts, transporting cables, moving 
air lines, and moving longwall roof support. 

4. Equipment maintenance.— Handling materials used 
during maintenance of mine equipment. Examples include 
extracting motors from continuous miners, replenishing 
hydraulic oil, and splicing cables. 

5. Mine maintenance.— Handling materials used in mine 
maintenance. Examples of activities include maintenance 
of roof, ventilation, rail track, and roadways. 

Table 7-5 lists some common underground mine 
materials and representative weights to give an idea of the 
kinds of loads that are often manually lifted, pushed, and 
pulled. 



91 



Table 7-5.— Common mine materials 
and their weights (75, 35), pounds 



Table 7-7.— Objects involved in overexertion back injuries 
suffered by underground coal miners during 1981 (31) 



Roof support supplies: 
Roof bolts, 5/8 in by 6 ft, 

bundle of 10 55 

Sheets, box of 25 25 

Plates, 6 by 6 by 1/4 in, 

bundle of 10 27 

Roof jack, 6 by 6 in by 5 

to 8 ft, closed 50-70 

Wood crossbars, 6 by 8 

in by 10 to 14 ft 160-225 

Round wood post, 6 in 

by 5 to 8 ft 48-76 

Metal "H" beam, 6 by 6 

in by 16 ft 320 

Rock dust, 1 bag 50 

Oil container, 5-gal (full) . . 40 

Brattice roll, 75-ft 60 



Trailing cable, 2- to 3-in 

diam, 10 ft long 50-100 

Concrete supplies: 

Cement, 1 bag 80-90 

Concrete block, 6 by 8 

by 16 in 

Rebar, 3/4 in by 6 ft, 

bundle of 10 

Rail supplies: 
Rail: 

30-lb, 30 ft 

60-lb, 30 ft 

Rail tie, 8 by 6 by 72 in 
Belt supplies: 
Belt roller, 6 by 42 in 
Belt chain, 8 by 9 by 
52 in 20-25 



62 



90 



300 

600 

90-100 

50 



Materials Handling Accidents 

Annually, materials handling is the leading accident 
classification in coal, metal, nonmetal, stone, and sand and 
gravel underground and surface mining and in all process- 
ing and preparation plants. Table 7-6 shows the number 
of materials handling nonfatal-days-lost injuries occurring 
in the industry in 1983, as determined by MSHA (36). 
Overall, materials handling accounted for 33.7% of all 
nonfatal-days-lost accidents in the mining industry that 
year. 



Table 7-6.— Materials handling nonfatal-days-lost (NFDL) injuries 
in the mininq industry, 1983 (36) 

(Courtesy of U.S. Mine Safety and Health Administration) 



Coal: 

Underground 

Surface 

Preparation plants 
Metal: 

Underground 

Surface 

Mills 

Nonmetal: 

Underground 

Surface 

Preparation plants 
Stone: 

Underground 

Surface 

Mills 

Sand and gravel surface . 
Overall 



NFDL 


Share of 


in- 


all in- 


juries 


juries, % 


2,432 


35.1 


439 


28.8 


236 


36.8 


162 


24.0 


103 


31.6 


175 


35.6 


82 


33.7 


50 


33.3 


236 


41.2 


16 


21.9 


254 


32.2 


376 


36.3 


164 


29.9 


4,725 


33.7 



Materials handling injury reports covering a 3-yr period 
showed that 40% involved injury to the back (11). Finger 
injuries while handling materials were the next most 
prevalent (18%). It was also found that over half of the in- 
juries (52%) involved overexertion; of these, 60% occurred 
while lifting objects. Table 7-7, for example, lists the type 
of objects underground coal miners were attempting to move 
when they incurred back injuries because of overexertion. 
(31). 



Electric cables 

Broken rock and coal . . . 

Timbers and posts 

Metal objects' 

Belt conveyor systems . . 

Wood objects 2 

Steel rails 

Bagged materials 

Jacks 

Mining machines 

Roof bolts 

Oil containers 

Cement blocks 

Buckets and cans 

Metal covers and guards 

Pry bars 

Motors 

Wheels 

Boxes 

Other 



Total 




100.0 



1 Does not include metal objects such as rails, roof bolts, jacks, motors, etc., 
which are listed separately. 

2 Does not include timbers, posts, caps, and headers. 



Materials handling accidents at 27 underground coal 
mines during 1973 were analyzed (16). As shown in figure 
7-12, the majority of injuries occurred in production supply 
activities. This high number is probably due to several fac- 
tors, including (1) materials are often handled several times 
from the yard to locations near the face, thus increasing 
exposure to injury; (2) many shipments of materials are 
made on a daily basis, again increasing injury exposure; 
and (3) materials are often banded or tied together in large, 
heavy packages, thus increasing the risk of injury. 

Biomechanics of Lifting 

Because a majority of materials handling injuries result 
in back injury from overexertion, and most of these occur 
during lifting activities, a review of the basic dynamics of 
lifting and back injury is in order. Biomechanics is the 
science that, among other things, considers the actions of 
the human body in bringing about controlled movements 
and applying forces, torques, energy, and power to exter- 
nal objects (32). 

The basic principle of lifting involves the physics of 
levers. When a load is held in the hands, the load as well 
as the person's body mass creates rotational movements or 
torques at the various joints of the body. The skeletal 
muscles are positioned to exert forces at these joints to 
counteract the movements due to the load and body weight. 
The problem is that the muscles are positioned so that they 
act through relatively small moment arms. Consider the 
example depicted in figure 7-13 where a 10-kg (22-lb) weight 
is held in the hand with the elbow at a 90 ° angle. For the 
arm to maintain its position, the bicep muscle must exert 
a force sufficient to overcome the weight of the load and 
the weight of the forearm and hand. Based on anthropo- 
metric data for an average male, the forearm weighs 
approximately 4.4 lb. For the average male, the biceps mus- 
cle is attached 2 in. from the point of rotation of the elbow, 
the length of the forearm is approximately 14 in, and the 
center of gravity of the forearm and hand is approximately 
6.7 in. from the elbow. This is shown in simplified form in 
the lower half of figure 7-13. 



92 



140 



120 



100 



[2 80 

Z 
UJ 

9 
o 

O 60 



40 



20 



I33((50%) 



KEY 
A Production supply 
8 Equipment maintenance 
C Section move 
D Production end use 
E Mine maintenance 
Total accidents, 269 



44(16%) 



35(13%) 



30(11%) 



27(10%) 



° A B C D E 

MINING ACTIVITY 

Figure 7-12. — Materials handling accidents by major activity 
or function. Data are from 27 coal mines during 1973. 




b*® 



MO kg 



£. 



Tf a ~~|f l 

— d a -H 



F M 
Fa 

Fl 
Dm 

Da 



KEY 
Muscle force 

Force from weight 
of arm and hand 

Force from load 

Distance of muscle 
force 

Distance of hand 
and arm 

Distance to load 



Figure 7-13.— Illustration of basic muscle biomechanics and 

lever analog (27). (Courtesy of National Institute for Occupational Safety and Health) 



The moment or torque created by each load is the prod- 
act of its force (a weight) and the distance from its center 
of gravity to the rotation or pivot point. As with a teeter- 
totter, to balance a light and heavy person, the light per- 
son should sit at the end of the teeter-totter arm and the 
heavy person nearer the pivot point. The light weight and 
long distance compensate for the heavy weight and short 
distance. 

The force the biceps muscle in figure 7-13 must exert 
to hold the 22-lb weight can be calculated using the follow- 
ing formula: 

(F M x D M ) = (F L x D L ) + (F A x D A ), 

where: F = force, lb, 

D = distance from the force to the pivot point, in, 

M = muscle, 

L = load being held, 

and A = arm. 

The solution is 

(F M x 2) = (22 x 14) + (4.4 x 6.7) or F M = 169 lb. 

Therefore, even in this simple situation, the biceps must 
exert a force more than seven times the weight of the ob- 
ject being held. In addition, when a muscle pulls across an 
extended joint, it compresses the joint with about the same 
magnitude of force. This is an important concept when con- 
sidering low-back biomechanics. 

The spine is made up of a series of bony vertebras 
stacked up with flexible fibrous pads, called disks, between 
each one. As shown in figure 7-14, the spinal column is 
divided into five sections, and the vertebras in each section 
are numbered for easy reference (19). 

Most back injuries occur in the lower lumbar spine, and 
the LvS, disk (sacrovertebral joint) has been used to repre- 
sent the spinal stresses of lifting. Biomechanical models 
have shown that during the lifting of a weight, the bending 
moment at the L 5 -S, joint can become quite large due, in 
part, to the weight of the upper body. For example, lifting 
a 110-lb weight from the floor can produce a bending mo- 
ment of approximately 1,732 lb-in at the L 5 -S, joint, accord- 
ing to NIOSH (27). To counteract this moment, the muscles 
of the lower back region (i.e., the erector spinae group) must 
exert large forces because they operate on very small mo- 
ment arms (approximately 2 in). Thus, to produce 1,732 lb- 
in, the muscles must exert a force of 8801b. The large forces 
generated by the lower back muscles are the primary 
sources of compression forces on the Lj-Sj disk. The only 
force that acts to diminish the compression forces of the 
spine is intra-abdominal pressure. 

Figure 7-15 shows the results of an analysis of the back 
muscle force and compression forces resulting from lifting 
a 100-lb timber in the posture depicted. The resulting mus- 
cular force on the back in this situation was 1,148.5 lb and 
the compression force on the L 5 -S, disk was 1.219.6 lb. 

The amount of compressive force that the vertebras can 
tolerate before experiencing microfractures is a function of, 
among other things, age. sex, and prior compressive stresses 
experienced. Data from cadavers of males under 40 yr of 
age show a mean of about 1,485 lb of compression required 
before microfractures occur. The value drops to approxi- 
mately 880 lb for males 50 to 60 yr old. There is. however. 
considerable individual differences in compression tolerance 
within any age group. It has been estimated by Sonoda (34) 



93 



Cervical 


Atlas * 
Axis 




/I 


Thoracic « 


F be 


Lumbar - 


■. y. 

> -'- • y- 


Sacral 


y? 

/r , 


Coccygeal 


*-/ 



C4 



T 4 
T 5 



'10 




Jl2 



L 2 



Sacrovertebral 
joint 

Articular portion 
of sacrum 



Figure 7-14.— Diagram of spinal column showing division and 

naming convention Of vertebras (19). (Courtesy of W.B. Saunders Co.) 



Back muscle tension, F 2 
(F 2 =l t l48.5lb) 




w,=30lb 



(738.2 lb) 



rw N Reaction, R 
^ (R=l,2l9.6lb) 

(970.8 lb) 



F, = IOOlb 



w | = Weight of head, neck, and arms (estimated as a 
percent of total body weight) 

w 2 = Weight of trunk (estimated as a percent of total body 
weight) 

F|=External weight lifted or held (timber) 

Figure 7-15.— Calculated lower-back muscle force and com- 
pressive (reactive) forces acting on L 5 -S, disk resulting from 

lifting a timber post (6). (Copyright 1983 by the Human Factors Society Inc., 
and reproduced by permission) 



that the female spinal compression tolerance is about 17% 
less than that of males due, in part, to the smaller force- 
bearing area of their vertebras. 

According to NIOSH (27), the following is the current 
view on the genesis of a ruptured disk. Repeated compres- 
sive stresses, especially from lifting, are sufficient to cause 
microfractures in the cartilage end plates and subchondral 
bone of the vertebras, which it is believed alters the me- 
tabolism and fluid transfer to the disk. If this occurs, the 
disk begins to degenerate, and its capacity to withstand fur- 
ther compression loads decreases. The result is that the disk 
squeezes out from between the vertebras and presses on the 
spinal nerve root as shown in figure 7-16. This is commonly 
called a slipped or ruptured disk. 

If this scenario is correct, then assigning cause for lower 
back pain to the immediate circumstance at the time when 
the pain first developed may be overly simplistic. In fact, 
most low-back injuries do not suddenly start with a jabbing 
pain, although such cases are easily remembered. Most 
often, the symptoms are slow to develop, with stiffness, dull 
aching pain, and finally incapacitating discomfort that can 
occur hours or days later. 

Effects of Lifting Posture 

The most important rule in lifting is to bring the torso 
(really the L 5 -S! joint) as close as possible to the center of 
gravity of the load before lifting. The closer the L 5 -S! joint 
is to the load, the shorter the moment arm and the lesser 
the force applied to the back. A second and subordinate prin- 
ciple, is that the back should be kept straight and vertical 
during a lift. In that posture, the compressive forces on the 
spine are more or less evenly distributed over the load- 
bearing surface of the vertebras. When the trunk is allowed 
to bend forward, the forces are concentrated on the front 
edges of the vertebras and tend to squeeze the disk toward 
the rear of the vertebral column. 

The best posture for lifting depends partially on the size 
of the load being lifted. Small loads that can fit between 
the knees when in a squat posture are best lifted with the 
classical bent knee-straight back technique. With the load 
between the knees, the torso is very close to the load center 
of gravity, and the strain on the back is reduced. In addi- 
tion, the back is kept vertical. Although this is often the 




Normal 



Ruptured 



Figure 7-16.— Cutaway view of ruptured L5-S1 disk pressing 
the spinal nerve (8). 



94 



recommended lifting method, it may be easier said than 
done. Often, people do not have the upper leg strength 
needed to lift the load and the weight of the body. Because 
the body must be lifted in this technique, it is one of the 
most costly in terms of energy expenditure, and it quickly 
induces fatigue if adequate rest periods are not taken. In 
addition, this squat-lift technique requires flexibility and 
ranges of motion in the hips, knees, and ankles that many 
people do not possess. A systematic exercising and stretch- 
ing program may be required to build the strength and flex- 
ibility needed to use this type of lift. Finally, it is often not 
possible to get close to the load being lifted to perform a 
bent-knee lift because of obstructions. 

When an object to be lifted is large (not necessarily 
heavy), then the squat lift may be more dangerous than the 
stoop-back lift technique, where knees are only slightly 
flexed, and the person bends over at the waist to lift the 
object. If a squat lift is attempted on a large object, the knees 
will not fit around it, and the object will have to be lifted 
in front of the knees. This places the load further from the 
L^-Sj joint and increases the compressive forces on the disk. 
Figure 7-17 shows a comparison of the two techniques while 
lifting a wide box (29). The stoop-back lift results in about 
two-thirds as much compression force as the squat lift. Ac- 
tually, the difference would be greater if the person moved 
in over the load even more than pictured in figure 7-17. 

Thus, the best lifting technique, from a biomechanical 
point of view, depends on the strength and mobility of the 
lifter and the dimensional size of the object to be lifted. The 
main idea is to keep the load close to the L 5 -S, joint. 

Another technique of lifting, called asymmetric lifting, 
is one to avoid. In this technique, the person brings the load 
up along the side of the body with one hand. This not only 
causes lateral (side-to-side) bending of the lumbar column, 
but because of the natural arc of the lower back, also pro- 
duces a rotation of each vertebra on its adjacent vertebra. 
This is especially hard on the disks between the vertebras 
and concentrates stress on the muscles used to stabilize the 
spinal column. 



disk compression = 
183.3 kg 



L 5~ s i 
disk compression 1 

278.5 kg 




Body weight 
above L 5 -S, 
center of gravity 



Stoop- back lift 



Squat lift 



Figure 7-17.— Comparison of lower-back compression forces 
associated with stoop-back and squat methods of lifting a wide 

Object (29). (Copyright 1974 by the American Institute of Industrial Engineers, and 
reprinted by permission) 



NIOSH Recommended Lifting Load Limits 

NIOSH formulated a method for determining maximum 
load limit recommendations for lifting tasks (27). A lifting 
task is defined as "the act of manually grasping and rais- 
ing an object of definable size without mechanical aids." 
A lifting task, under this definition, takes normally less 
than 2 s to complete. This is in contrast to a holding or 
carrying task that requires sustained exertion. 

The recommendations are intended to apply only for- 

1. Smooth lifting; 

2. Two-handed, symmetric lifting directly in front of the 
body with no twisting during the lift; 

3. Moderate width objects, e.g., 30 in or less; 

4. Unrestricted lifting posture; 

5. Good couplings (handles, shoes, floor surface); and 

6. Favorable environments. 

In addition, the recommendations do not include safety 
factors to assure that unpredicted conditions are 
accommodated. 

Given the nature of the mining environment, many of 
the characteristics of the lifting tasks listed are often not 
present, especially in the underground environment. Pos- 
ture is often restricted, floors are often slippery, environ- 
ments are often hostile, and load widths are often larger 
than 30 in. It is important, therefore, to consider the NIOSH 
recommendations as best case limits. Any prudent mine 
superintendent or supervisor should reduce the recom- 
mended limits to compensate for unfavorable lifting 
situations. 

The NIOSH recommendations take into account five 
parameters of the lifting task to determine the load limits. 
Two limits are defined: the maximum permissible limit and 
the action limit, which is one-third the maximum permis- 
sible limit. Situations that are above the maximum per- 
missible limit are considered unacceptable and require 
redesign of the task. Situations below the action limit are 
considered acceptable for most of the workforce. Situations 
that fall above the action limit, but below the maximum 
permissible limit are considered unacceptable, unless the 
task is redesigned or a selection and training program is 
used to upgrade the capabilities of the workforce. 

The NIOSH (27) formula for determining the action 
limits for a given lifting situation and the determination 
follow. The maximum permissible limit is taken as three 
times the action limit. Table 7-8 shows the maximum lift 
frequency based on the average vertical location at the 
origin of the lift and the period of time for which the lift 
is performed. Horizontal location (H) = 6/H; vertical loca- 
tion (V) = 1 - (0.01 x |V-30|); vertical distance traveled 
(D) = 0.7 + (3/D); frequency of lift = 1 - (F/F^); and 
constant = 90. 

AL = 90 x H x V x D x F. 

where AL = action limit, lb, 

90 = constant, 

H = horizontal location forward of midpoint be- 
tween ankles at origin of lift, 6 to 32 in. 

V = vertical location at origin of lift, to 70 in, 

D = vertical travel distance between origin and 
destination of lift, 10-in minimum. 

F = average frequency of lift, lifts min. consid- 
ering maximum lift frequency, F max (from 
table 7-8), 
and F max = maximum lift frequency that can be sus- 
tained (.from table 7-8). lifts min. 



95 



Table 7-8.— Maximum lift frequency based on average vertical 
location and period of performance, lifts per minute 



Av vertical location 


in 


>30 


<30 






1 h or less 


18 
15 


15 


More or less continuous 
during shift 


12 







The maximum permissible lift is three times the action 
limit. An example of determining the action limit and max- 
imum permissible lift follows. 

Situation.— A worker lifts 36- by 18- by 8-in rock dust bags 
(50 lb each) from a scoop shovel on the ground and stacks 
them three high on a bin pallet. The first tier is 6 in off 
the ground, the second is 14 in off the ground, and the third 
tier is 22 in off the ground. The task is performed for less 
than 1 h at a rate of five bags lifted per minute. 

Analysis.— Although the vertical location, V, at the origin 
of the lift is the same throughout the task, the vertical 
travel distance, D, varies from 6 to 22 in, depending on the 
tier. One approach would be to perform the analysis on each 
tier separately as if it were a separate task. Another ap- 
proach, used here, is to determine an average travel 
distance (i.e., 6 + 14 + 22 = 42, 42/3 = 14) and apply the 
action limit formula to the average task. The horizontal 
location, H, is estimated to be 6 in plus half the width of 
the object (i.e., 6 + 18/2 = 15). 

Calculations.— Constant is 90; horizontal location factor, 
H, is 6/15 or 0.40; vertical location factor, V, is 1 - (0.01 
x 30) or 0.70; vertical travel distance factor, D, is 0.7 + 
(3/14) or 0.91; maximum frequency, F max , from table 7-8, is 
15; and frequency of lift factor, F, is 1 - (5/15) or 0.67. Us- 
ing the action limit formula, AL is determined as follows: 
AL = 90 x 0.40 x 0.70 x 0.91 x 0.67, which yields 15.4 
lb. The maximum permissible lift (3 x AL) is 46 lb. 

Conclusion:— Since the rock dust bags weigh 50 lb, the 
AL is 15.4 lb, and the maximum permissible lift is 46 lb, 
this task would be unacceptable under the best of circum- 
stances and the task should be redesigned. 

REDUCING THE RISK 

The risks inherent in a manual materials handling task 
can be reduced by redesigning the task, redesigning the 
workspace, selecting physically capable people to do the 
task, training workers involved in normal materials han- 
dling tasks, or a combination of these methods. 

The following are methods for reducing the physical 
stresses involved in manual materials handling tasks, the 
fundamental concept being that active awareness of the 
problem and a conscious effort to reduce the physical 
stresses involved in the task can accomplish significant 
results without incurring significant costs. 

Redesign the task: 

1. Use lifting aids (e.g., hoists, cranes, rollers, jacks, 
conveyors). 

2. Reduce weight of object. 

3. Reduce frequency of lifting (lifts per minute). 

4. Reduce duration of task (hours per shift). 

5. Reduce the size of the object being handled. 

6. Supply properly designed handles on the objects being 
handled. 

7. Maintain a predictable center of gravity in the load 
being lifted. 



Redesign the workspace: 

1. Remove obstructions that prevent worker from getting 
close to the object being lifted. 

2. Provide ample space to maneuver and assume most 
advantageous lift posture. 

3. Begin lifts at about elbow height. 

4. Reduce vertical travel requirements for lift. 

5. Provide slip-resistant soles and floors. 

6. Provide good lighting. 

7. Maintain comfortable temperature, humidity, and 
airflow. 

Select workers: 

1. Strength testing. 

2. Aerobic capacity testing. 

3. Clinical examination. 
Train workers: 

1. Hazard awareness. 

2. Biomechanics of manual materials handling. 

3. Reducing hazards. 

4. Physical fitness. 

Redesign the Task 

The use of lifting aids is an obvious way to reduce the 
physical strain on the job. Often, a little forethought can 
make the use of such devices easier and safer to use. For 
example, if materials are transferred at the cage or skip, 
the area should be designed to accommodate lift trucks and 
cranes. If components must be removed for maintenance in 
a processing plant, fixtures should be installed so that tem- 
porary winches can be attached. Floors should be smooth 
so that rollers and dollies can be easily used. 

Reducing the weight of the load is an obvious solution 
to the problem, yet is often overlooked. The 50-lb rock dust 
bags might be purchased in 25-lb bags. In addition, the 
smaller bags would be more compact and hence permit the 
worker to get closer to the load to lift it. To illustrate this 
effect, if the width of the rock dust bags described in the 
action limit determination were reduced from 18 to 12 in, 
the action limit would increase from 15.4 to 19.2 lb. In ad- 
dition to the overall weight, the center of gravity of the load 
should be predictable and nonshifting. A box, half filled with 
supplies that shift when lifted, places asymmetric loads on 
the back and increases the probability of falls. The use of 
baffles, dividers, or packing to stabilize the center of gravi- 
ty is recommended. 

The proper placement and design of handles can reduce 
biomechanical strain and reduce the chances of dropping 
the load. In general, handles should be placed above the 
center of gravity, unless the height of the load would inter- 
fere with the legs during walking. Many handles in use 
today are unsatisfactory because of insufficient hand 
clearance, sharp edges that can cut into a worker's hand, 
and handle diameters that are too small. 

Handle width should be at least 4.5 in with a 2-in 
clearance all around the handle. If gloves are worn during 
lifting, clearance should be at least 3 in, and the handle 
should be 5.5 in. Handle diameter should be between 1 and 
1.5 in. 

Redesign the Workspace 

Often, a simple rearrangement of the workspace will 
permit a worker to get closer to an object when lifting and 
releasing it. The use of platforms on which to stack mate 
rials can bring the lifting task to elbow height and require 



96 



little or no vertical movements. In the action limit deter- 
mination, if the scoop shovel were lifted to the same height 
as the stacked rock dust bags, and if the bags were stacked 
on a pallet 22 in high (instead of 6 in), then the action limit 
would be increased from 15.4 to 24.1 lb, and the maximum 
permissible limit would be 72 lb. Thus, the task would be 
acceptable. 

Good lighting and slip-resistant soles and floors, of 
course, reduce trip and slip-and-fall accidents. Comfortable 
temperature, humidity, and airflow are especially impor- 
tant for continuous physical activity since heat adds a con- 
siderable burden to the circulatory system, and when added 
to the strain from the physical task, can be dangerous. 

Selection of Workers 

Any methods for selecting workers for physically 
demanding tasks should meet the following criteria: 

1. Be safe (if a physical test of abilities is used). 

2. Produce reliable results. 

3. Be related to the specific demands of the task. 

4. Be practical to administer. 

5. Predict risk of future injury or illness. 

Most of these are obvious; however, the methods used 
to select workers must be related to the specific demands 
of the job in order to eliminate accusations of bias in selec- 
tion methods. Further, the job must be designed to reduce 
the physical demands to the lowest practical level, and the 
selection methods should be built around the redesigned job. 
Failure to redesign a job, consequently excluding females, 
might well be considered an act of discrimination. 

Methods for selecting workers for physically demanding 
tasks have centered around clinical examinations, strength 
testing, and aerobic capacity testing. A clinical examina- 
tion is a must for selecting workers for physically demand- 
ing tasks. The purpose is to uncover any abnormalities that 
might restrict the physical activity of a worker, and to iden- 
tify those with prior episodes of back pain. It was reported 
by Dillane (3) that the probability of an episode of back pain 
increases by a factor of 3 to 4 after the first reported attack. 

Some clinicians promote the use of lower-back X-rays 
as a means of evaluating the risk potential to an individual 
engaged in a lifting task. Current thinking, however, is that 
such X-rays are of little practical value in predicting future 
disability. Several studies, such as by NIOSH (27), report 
no significant differences in the incidence of radiologically 
identified abnormalities between workers with known his- 
tories of back pain and those without. Such X-rays, however, 
can be useful in conjunction with prior clinical examina- 
tions to corroborate a suspected diagnosis. 

Considerable attention has been given to the use of 
strength testing as a means of selecting workers for 
demanding lifting tasks. For continuous, high-energy tasks, 
the measurement of aerobic capacity appears to be a valu- 
able selection device. Specific methods for measuring 
strength for preemployment testing are discussed by Chaf- 
fin (8) and Kroemer (23). 

Ayoub (6) reported the use of a job severity index ( JSI) 
as a measure to match an individual with the demands of 
a lifting task. The JSI is the ratio of a measure of job de- 
mand to a measure of the capacity of the person perform- 
ing the job under the job conditions. The measure of lifting 
capacity is determined from formulas that predict the max- 
imum weight an individual feels he or she can lift re- 
peatedly without undue stress or overtiring. The formulas 
take into consideration the following factors: sex, weight, 



age, arm strength, back strengh, dynamic endurance, 
shoulder height, and abdominal depth. 

In a study of 101 jobs involving 385 males and 68 
females, Ayoub (6) found that as the JSI increased, the in- 
cidence and severity (days lost per incidence) of lower-back 
injuries increased (fig. 7-18). JSI values below 1.0 indicate 
that the worker's capability exceeds the demands of the job. 
JSI values greater than 1.0 indicate that the job demands 
exceed the capabilities of the worker. As can be seen in 
figure 7-18, the number of incidents dramatically increases 
with JSI values greater than 1.5, and the severity of in- 
cidence dramatically increases with values greater than 
2.25. 

Training Workers 

Although training for manual materials handling has 
been practiced in some European countries since World War 
II, there appears to have been few, if any, controlled studies 
showing a drop in injury rates following training. Probably 
what has kept up the interest is that employers feel a legal 
or moral obligation to provide such training. The follow- 
ing is the NIOSH recommended (27) content for a training 
program on manual materials handling. 

1. Risks to health of unskilled manual materials handling 
(including accident experience of the organization). 

2. Basic physics of manual materials handling. 

3. Effects of manual materials handling on the body (in- 
cluding anatomy of spine and muscles and joints). 

4. Individual awareness of the body's strengths and 
weaknesses (including how much can be handled safely and 
comfortably). 

5. How to avoid accidents (including task design varia- 
bles, workspace layout, sizing up the load, planning the 
activity). 




OSJSK 0.75 0.75SJSKI.50 I.50SJSK2.2S E-25 < JSI 

JSI RANGE 

Figure 7-18. — Incidence and severity of back injury as a func- 
tion of the job severity index (JSI). JSI values greater than 1 .0 
indicate job demands exceed worker capabilities: values less 
than 1.0 reflect worker capacities exceed job demands (5). 

(Copyright 1983 by the Human Factors Society Inc.. and reproduced by permission) 



97 



6. Handling skill (including actually lifting, carrying, 
pushing, pulling materials handled on the job; the best way 
to perform each task; and the principles involved). 

7. Handling aids (including when to use them, how to use 
them, how to improvise). 

Examples of training materials for the mining industry 
based on the components listed above were developed by 
Connelly (10). 

NIOSH (27) also pointed out that an adequate training 
program must do more than just demonstrate the principles 
using slides or films; participants must be actively involved 
in the program. Teaching must extend beyond the classroom 
back to the worksites to be effective. 

Physical fitness training is another aspect of manual 
materials handling training, although it is not listed in the 
recommended course content by NIOSH. A 12-week pro- 
gram in which sessions were held twice per week was 
reported on by Chenoweth (9). The results showed small, 
but reliable improvements in heart rate, blood pressure, 
body weight, percentage of body fat, and flexibility. 

DISCUSSION 

Although manual materials handling injuries continue 
to be the major category of lost-time injuries in mining, an 
active awareness of the problem and an understanding of 
the principles and dynamics involved can go a long way 
toward reducing the hazards. Mining will continue to be 
a physically demanding occupation, but by proper design 
of the tasks and worksites and proper employee training 
and selection, the incidence and severity of injuries can be 
reduced. Proper task design will also contribute to a higher 
level of productivity by reducing the level of fatigue 
experienced by a worker. Much has been done to improve 
the work environment, and much still remains to be done. 



REFERENCES 

1. American Heart Association (New York). Exercise Testing and 
Training of Apparently Healthy Individuals: A Handbook for Physi- 
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2. American Industrial Hygiene Association Journal. Ergonomics 
Guides: Ergonomics Guide to Assessment of Metabolic and Car- 
diac Costs of Physical Work. Aug. 1971, pp. 560-574. 

3. Astand, P., and K. Rodahl. Textbook of Work Physiology. 
McGraw-Hill, 2d ed., 1977, 669 pp. 

4. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford, D.K. Cad- 
del, K. Intaranont, S. Morrissey, and J.L. Selan. Mining in Low 
Coal. Volume I: Biomechanics and Work Physiology (contract 
H0387022, Texas Tech Univ.). BuMines OFR 162(l)-83, 1981, 175 
pp.; NTIS PB 83-258160. 

5. Biomechanics and Work Physiology in Low Coal. 

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December 3, 1981; St. Louis, Mo., December 10, 1981; and Denver, 
Colo., December 15, 1981; comp. by Staff, Pittsburgh Research 
Center. BuMines IC 8866, 1981, pp. 3-16. 

6. Ayoub, M., J. Selan, and D. Liles. An Ergonomics Approach 
for the Design of Manual Materials Handling Tasks. Human Fac- 
tors, v. 25, No. 5, 1983, pp. 507-515. 

7. Brown, J. Lifting as an Industrial Hazard. Ontario Dep. of 
Labor, Toronto, Canada, 1971, 16 pp. 

8. Chaffin, D. Preemployment Strength Testing. J. Occup. Med., 
v. 20, No. 6, 1978, pp. 403-408. 

9. Chenoweth, D. Fitness Program Evaluation: Results With 
Muscle. Occup. Health and Safety, June 1983, p. 14. 



10. Connelly, D. A Manual Materials Handling (MMH) Train- 
ing Program for the Mining Industry. Paper in Back Injuries. 
Proceedings: Bureau of Mines Technology Transfer Symposia, Pitts- 
burgh, PA, August 9, 1983; and Reno, NV, August 15, 1983; comp. 
by J.M. Peay. BuMines IC 8948, 1983, pp. 74-80. 

11. Conway, E., and W. Elliott. Back Injuries and Maintenance 
Material Handling in Low-Seam Coal Mines. Paper in Back In- 
juries. Proceedings: Bureau of Mines Technology Transfer Sym- 
posia, Pittsburgh, PA, August 9, 1983, and Reno, NV, August 15, 
1983; comp. by J.M. Peay. BuMines IC 8948, 1983, pp. 74-80. 

12. Davies, B. Moving Loads Manually. Appl. Ergonomics, v. 3, 
No. 4, 1972, pp. 190-194. 

13. Dillane, J, J. Fry, and G. Kalton. Acute Back Syndrome. Brit. 
Medical J., v. 2, 1966, pp. 82-84. 

14. Edholm, O. The Biology of Work. McGraw-Hill, 1967, 267 pp. 

15. Ellis, C. Accidents Related to Transportation and Materials 
Handling. Paper in Proceedings of 14th Annual Institute of Coal 
Mining Health and Safety Research. Polytechnic and State Univ., 
Blacksburg, Va., Aug. 23-25, 1983, pp. 106-121. 

16. Foote, A.L., and J.S. Schaefer. Mine Materials Handling 
Vehicle (MMHV) (contract H0242015, MBAssoc). BuMines OFR 
59-80, 1978, 308 pp.; NTIS PB 80-178890. 

17. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
Approach. Taylor and Francis, 1981, 379 pp. 

18. Hamilton, B., and R. Chase. A Work Physiology Study of the 
Relative Effects of Pace and Weight in Carton Handling Tasks. 
AIIE Trans., v. 1, 1969, pp. 106-111. 

19. Jacobs, S., and C. Francone. Structure and Function in Man. 
Saunders, 5th ed., 1965, 538 pp. 

20. Kamon, E. Laddermill and Ergonometry: A Comparative 
Summary. Human Factors, v. 15, No. 1, 1973, pp. 75-90. 

21. Kamon, E., and M. Ayoub. Ergonomic Guides: Ergonomic 
Guide to Assessment of Physical Work Capacity. Am. Ind. Hygiene 
Assoc, Akron, Oh., 1976, 9 pp. 

22. Khalil, T. An Electromyographic Methodology for the Evalua- 
tion of Industrial Design. Human Factors, v. 15, No. 3, 1973, pp. 
257-264. 

23. Kroemer, K. Field Testing of Workers Involved in Material 
Handling. Paper in Back Injuries. Proceedings: Bureau of Mines 
Technology Transfer Symposia, Pittsburgh, Pa., August 9, 1983, 
and Reno, Nev., August 15, 1983; comp. by J.M. Peay. BuMines 
IC 8948, 1983, pp. 47-53. 

24. Morrissey, S., N. Bethea, and M. Ayoub. Task Demands for 
Shovelling in Non-Erect Postures. Ergonomics, v. 26, No. 10, 1983, 
pp. 947-951. 

25. Muller, E. The Physiological Basis of Rest Pauses in Heavy 
Work. Q. J. Experimental Physiology, v. 38, 1953, p. 205. 

26. Murrell, K. Human Performance in Industry. Reinhold, 1965, 
306 pp. 

27. National Institute for Occupational Safety and Health. Work 
Practices for Manual Lifting. NIOSH Publ. 81-122, 1981, 183 pp.; 
NTIS PB 82-178948. 

28. Pafnote, M., I. Vaida, and O. Luchian. Physical Fitness in 
Different Groups of Industrial Workers. Physiologie, v. 16, No. 2, 
1979, pp. 129-131. 

29. Park, K., and D. Chaffin. A Biomechanical Evaluation of Two 
Methods of Manual Load Lifting. AIIE Trans., v. 6, 1974, pp. 
105-113. 

30. Peay, J. Introduction. Section in Back Injuries. Proceedings: 
Bureau of Mines Technology Transfer Symposia, Pittsburgh, Pa., 
August 9, 1983, and Reno, Nev., August 15, 1983; comp. by J.M. 
Peay. BuMines IC 8948, 1983, p. 2. 

31. Peters, R. Activities and Objects Most Commonly Associated 
With Underground Coal Miners' Back Injuries. Paper in Back In- 
juries. Proceedings: Bureau of Mines Technology Transfer Sym- 
posia, Pittsburgh, Pa., August 9, 1983; and Reno, Nev., August 15, 
1983; comp. by J.M. Peay. BuMines IC 8948, 1983, pp. 23-31. 

32. Roebuck, J., K. Kroemer, and W. Thomson. Engineering An- 
thropometry Techniques. Wiley, 1975, 459 pp. 

33. Sims, M., L. Morris, R. Graves, and G. Simpson. Manual 
Handling of Mining Materials. Paper in Proceedings of the 1984 
Int. Conf. on Occupational Ergonomics, Human Factors Assoc, of 
Canada. Toronto, Canada, May 7-9, 1984, pp. 103-118. 



98 



34. Sonoda, T. Studies on the Compression, Tension, and Tor- 
sion Strength of the Human Vertebral Column. J. Kyoto Prefect 
Medical Univ., v. 71, 1962, pp. 659-702. 

35. Unger, R., and D. Connelly. Materials Handling Methods and 
Problems in Underground Coal Mines. Paper in Back Injuries. Pro- 
ceedings: Bureau of Mines Technology Transfer Symposia, Pitts- 
burgh, Pa., August 9, 1983; and Reno, Nev., August 15, 1983; comp. 
by J.M. Peay. BuMines IC 8948, 1983, pp. 3-22. 

36. U.S. Mine Safety and Health Administration Quarterly. Mine 
Injuries and Worktime, January-December, 1983. 1984, 34 pp. 

37. Van Rensburg, J. Energy Requirements of Different 
Underground Mining Tasks With Specific Reference to the In- 



fluence of Mechanization. Chamber of Mines, Johannesburg, South 
Africa, Rep. No. 11/81, Mar. 1981, 61 pp. 

38. Weiser, P. Interrelationships of the Motor and Metabolic Sup- 
port Systems During Work and Fatigue. Ch. in Psychological 
Aspects and Physiological Correlates of Work and Fatigue, ed. by 
E. Swanson and P. Weiser. Charles C. Thomas, 1976, pp. 212-255. 

39. Wyndham, C, and G. Sluis-Cremer. The Capacity for 
Physical Work of White Miners in South Africa. South African 
Medical J., v. 43, No. 1, 1969, pp. 3-8. 



99 



CHAPTER 8.— ENVIRONMENTAL FACTORS 





In addition to the obvious environmental factor of temperature, illumination and noise factors, as 
well as others, affect the performance, health, comfort, and safety of miners. 



Humans live and work in a wide range of environments, 
each with its own set of particular characteristics that can 
affect performance, health, comfort, and safety. Because the 
list of such environmental factors is extensive, including 
odors, dust, chemical fumes, radiation, and even insects, this 
chapter will only concentrate on four factors that are tradi- 
tionally covered in the human factors literature: illumina- 
tion, noise, whole-body vibration, and climate (heat and cold 
stress). For each of these factors, a brief discussion is pre- 
sented covering the measurement of the factor, conditions, 
found in mining, effects of the factor on humans, standards 
that exist, and methods for reducing the negative effects 
of the factor on workers. 



ILLUMINATION 

The topic of illumination is especially important in the 
mining environment. Underground mines are completely 
dependent on artificial sources of illumination, as are night 
operations in surface mines. Because humans receive the 
bulk of their information visually, the quantity and qual- 
ity of illumination is critical to the safe and efficient per- 
formance of our jobs. 

Measurement of Light 

Two major systems of units are currently used for the 
quantification of light: English system and International 



100 



System of Units (SI). The primary difference between the 
English and SI systems is that the English system uses U.S. 
standard measures for linear dimensions in the unit defini- 
tions, while the SI system uses metric measures. Current 
U.S. coal mine lighting regulations customarily use English 
units; therefore, these will be used primarily in this section. 
All standard systems of light units employ the follow- 
ing basic concepts: 

1. Luminous Flux (<(>, unit— lumens, lm).— The time rate 
flow of light energy. 

2. Illuminance (E, unit— footcandle, fc, or lux, lx).— A 
measure of the density of luminous flux striking a surface. 

3. Luminous Intensity (I, unit— candle, c).— A concept used 
to describe how a light source distributes the total luminous 
flux, or lumens, it emits into various portions of the space 
surrounding the source. 

4. Luminance (L, unit— candle per square inch, c/in 2 , or 
candle per square meter, dm 2 ).— In physical terms, lumin- 
ance is a concept used to quantify the density of luminous 
flux emitted by an area of a light source in a particular 
direction toward a light receiver, such as an eye. 

5. Reflectance (q).— The ratio of reflected to incident light 
energy, which may be defined as lumens emitted per unit 
area divided by lumens incident per unit area. 

6. Contrast.— The concept that the greater the luminous 
and color contrasts of an object with its background, the 
greater the object visibility. 

Luminous Flux 

Flux is a power quantity in the same manner as horse- 
power or Btu per hour. The unit of luminous flux, the lumen, 
is most frequently used to describe the total lighting power 
of light sources. 

Illuminance 

Imagine a light source placed inside, at the center of 
a sphere. The amount of light striking any point on the in- 
side of the sphere is called illuminance. It is measured in 
terms of luminous flux (per steradian) 1 per unit surface. One 
lumen per square foot is equal to 1 fc, and 1 fc is equal to 
10.76 lx. An accepted practice for some purposes is to con- 
sider 1 fc equal to 10 lx, ignoring the fraction (23)} 

The amount of illuminance striking a surface from a 
light source follows the inverse square law, E = I/D 2 , where 
D is the distance from the source. At 2 ft, a 1-c source would 
produce 1/4 fc; and at 3 ft, it would produce 1/9 fc. 

Luminous Intensity and Luminance 

Some light striking a surface is reflected. The amount 
of light (luminous intensity) per unit area leaving a sur- 
face is called luminance. Luminance is defined in terms of 
lumens (luminous flux per steradian) per square foot, or 
footlambert. 

Reflectance 

The ratio of reflected luminous flux to the total incident 
luminous flux is reflectance. Some surfaces reflect, while 
others absorb almost all the luminous flux that strikes 



them. Generally, dark-colored surfaces absorb more lum- 
inous flux than do light-colored surfaces. 

In actuality, no surface is a uniform diffusing surface. 
The reflectance of 34 wet and dry rock and mineral samples 
from underground metal and nonmetal mines was meas- 
ured by Crooks (11). Table 8-1 presents some representative 
data from that survey. Notice that wet samples show lower 
average reflectance than dry samples. Over three-fourths 
of all worksites measured by Crooks (11) had reflectances 
of less than 30% . To illustrate the consequences of different 
reflectivity on the amount of illumination needed, Crooks 
and Peay (12) indicated that the lighting adequate for 
development activities in dry dolomite would have to be in- 
creased approximately 400% to achieve the same luminance 
levels in wet sphalerite. 



Table 8-1.— Examples of average reflectances 

of rocks and minerals from underground metal 

and nonmetal mines (11). percent 



Sample description 

Light brownish gray trona 

Brownish gray trona 

Feldspar with olivine, chalky surface . . . 
Feldspar with pyrite, medium gray color 

Dolomite 

Almost pure sphalerite 

Whitewashed shale (haulageway wall) . . 

Quartzite 

Chalcopyrite 



Dry 



Wet 



59 


28 


38 


19 


61 


38 


39 


24 


59 


44 


16 


9 


82 


61 


17 


11 


14 


8 



1 The steradian is a measure of the unit solid angle at the center of a 
sphere. There are 4 n or 12.57 sr in a sphere. 

2 Italic numbers in parentheses refer to items in the list of reterences at 
the end of this chapter. 



Contrast 

Althougn contrast is not a light measure per se. it is 
a critical concept for determining visibility. If an object has 
no contrast with its background, it will not be seen, regard- 
less of how much illuminance is supplied. Luminous con- 
trast is measured by the following formula: 

Contrast - Q D J ect luminance - Background luminance . 
Background luminance 



With more light, the eye can see detail better and. hence, 
less contrast is needed. For example, an object with lumin- 
ance of 43.8 fL on a background having a luminance of 14.6 
fL will be easier to see than an object with luminance of 
4.5 fL on a background having a luminance of 1.5 fL. even 
though both have contrasts equal to 2.0. Experiments have 
shown that a 1% loss of contrast requires a 10% to 15% in- 
creasejn illuminance to maintain the same visual perfor- 
mance (15). 

In addition to luminous contrast, color contrast also 
enhances visibility, even if the luminous contrast is zero. 
For example, a yellow target shows up against a blue back- 
ground, even if the luminance of the two colors is the same. 

Illumination and Performance 

At the turn oi tne ceniui j . coal miners commonly suf- 
fered from an eye disease called nystagmus. The symptoms 
were uncontrollable oscillations of the eyeballs, headaches, 
and dizziness. One of the main contributing factors was the 
effect of working under very low levels of light for long 



101 



periods of time. With the advent of electric caplamps, the 
disease virtually disappeared. 

The literature on mine lighting with respect to acci- 
dents, production, and health was reviewed by Trotter (44). 
With respect to accidents, several European studies were 
cited that showed accident rates decreasing as much as 60% 
when the overall level of illumination was increased. 
Studies in industries other than mining supported the 
general conclusions that increased levels of illumination 
have a positive effect on accidents. 

With respect to the effects of lighting on productivity, 
numerous studies have been done using simple tasks, such 
as threading needles, to show that increasing illumination 
up to about 100 fc results in increased productivity and 
decreased errors. Trotter (44) cited two studies relating 
lighting to productivity in the mining environment. Adding 
general area illumination resulted in an increase of 17% 
to 26% in productivity, compared to similar sections of the 
mine where only caplamps were used. 

In the underground environment, caplamp illumination 
results in notoriously poor peripheral vision, because the 
beam is usually focused to a narrow spot. The addition of 
general lighting in such situations greatly enhances pe- 
ripheral vision and allows workers to see objects more 
quickly and at greater distances. For example, the effect 
additional background luminance had on the detection time 
of various targets, such as simulated rock cracks, tripping 
hazards, and rock movements was measured by Merritt (28). 
In all cases, the provision of additional background lumin- 
ance decreased detection time and errors. As an example, 
figure 8-1 shows the average response time to detect holes 
in the floor at a distance of 10 ft. With caplamp illumina- 
tion only (0.055 fL), response time was 15 s. The provision 
of additional background luminance with general area light- 
ing decreased the response time to 1 s. 

Thus, it appears that improved lighting can improve 
safety, productivity, and the time needed to respond to 
hazards. Recognition of these facts has prompted govern- 
ment agencies to specify illumination requirements, which 
are discussed in the following section. 

Illumination Requirements 

The setting of illumination requirements involves many 
tradeoffs, including weighing the cost of increased illumina- 
tion against the improvement in visual performance, and 
balancing increased levels of illumination against the in- 
crease in glare. Trotter (44) reviewed standards set by var- 
ious countries for underground coal mining. The minimum 
light levels specified vary considerably from country to 
country, as shown in table 8-2. The data in table 8-2 are 
given in terms of illuminance (i.e., the amount of light strik- 
ing a surface). The United States and the Commission Inter- 
Table 8-2.— Samples of illumination standards set 
by various countries for underground coal mining (44), lux 





Shaft 


Loading 


Around machines 


Haulageways 


Belgium 


20- 50 


20 


25 


10 


British Columbia, 










Canada 


53 


21 


53 


21 


Czechoslovakia 


15- 40 


20 


20 


5 -10 


Germany, Federal 










Rep. of 


30- 40 


40 


80 


15 


Hungary 


40-100 


40-60 


20-50 


2 -10 


Poland 


15- 50 


15-30 


NA 


.5- 2 


United Kingdom .... 


70 


30 


NA 


2.5 




0.02 0.04 0.06 

BACKGROUND LUMINANCE, fL 



0.08 



NA Not available. 



Figure 8-1 .—Effect of adding additional background luminance 
(area lighting) on speed of detecting holes in a floor at a distance 
of 10 ft (28). 



nationale de l'Eclairage (CIE), by contrast, specify minimum 
levels in terms of luminance (i.e., reflected light). It is more 
appropriate to state requirements in terms of luminance, 
because it is reflected light that allows us to see objects; 
and, depending on the reflectance of the surface, the same 
amount of incident light can result in very different levels 
of reflected light. Whitewashing an area, for example, can 
greatly increase luminance without increasing the number 
or intensity of light sources. 

The United States requires 0.06 fL of luminance in work 
areas and around equipment in underground coal mines. 
Specific details of the requirements for underground coal 
mines are contained in reference 45. The usual practice is 
to plan illumination systems based on an assumed reflec- 
tance of 0.04 in coal mines. A luminance requirement of 
0.06 fL, with a reflectance of 0.04, yields an illuminance 
requirement (light striking the surface) of 1.5 fc. The Mine 
Safety and Health Administration (MSHA) requirements 
recognize the problem of glare, especially in low-seam mines 
(under 48 in), and have reduced the size of the area around 
machines that must be illuminated to the minimum re- 
quired luminance. 

With respect to surface mining, MSHA proposed that 
all exterior areas related to draglines, shovels, and wheel 
excavators, where people regularly work and travel, be il- 
luminated to 5.0 fc. This area extends out 20 ft in all direc- 
tions from the machines. Areas beneath the boom, from 20 
ft out from the main frame to the furthest point the equip- 
ment can excavate or discharge material, must be illumin- 
ated to 1 fc. 



102 



Merritt (28) performed extensive research to determine 
illumination requirements for underground metal and non- 
metal mines. The recommendations are somewhat more 
complex than the requirements for coal mines. For exam- 
ple, he recommends 0.1284 fL at 8-ft viewing distance, 12 ° 
off axis; and 0.05 fL at 6-ft viewing distance, 22.5° off axis. 
It was believed that a more powerful caplamp could supply 
the needed luminance. Recommendations for illumination 
of mobile equipment operations include 0.10 fL on the floor, 
20 ft in front of the machine. 

In order to determine if an illumination system will 
supply the proper amount and distribution of light, it is 
necessary to simulate the situation and equipment, install 
the lights, and take the required measurements. The 
Bureau, however, has developed a computer model that uses 
representations of mining machinery and data on lumi- 
nance output characteristics of various lights to compute 
the level and distribution of illumination in the work area 
(19-20). The system is interactive so that different types of 
lights and light positions can be tested quickly and easily. 

Glare 

Illumination engineers distinguish two types of glare: 
disability glare and discomfort glare. Disability glare inter- 
feres with visibility and reduces visual performance. Dis- 
ability glare operates in two ways. In the first, a glare source 
reduces the contrast of a visual scene by causing a scatter- 
ing of light in the fluid of the eyeball. This scattering creates 
a veiling brightness on the retina that in turn reduces con- 
trast. The second mechanism by which a glare source re- 
duces visual performance is due to transient adaptation. The 
source causes a shift in the eye's adaptation or sensitivity 
to light. The glare source causes the eye to become adapted 
to a higher level of illumination and hence less sensitive, 
which makes it harder to see low-contrast or dimly lit ob- 
jects. The effect is similar to going into a dark movie theater 
on a sunny day. 

The disability glare factor (DGF) of various lighting 
arrangements on underground coal mining equipment was 
reported on by Whitehead (49). The DGF indicates the 
percentage of visibility still left, given the effect of glare. 
The higher the number, the less the disability glare effect. 
For a continuous miner operator, DGF values in four work 
positions varied from 1.8% to 100% using various light 
sources. The average DGF across all positions and light 
sources was 51%, a reduction of almost 50% in visibility 
due to disability glare. An even poorer situation was 
reported for a roof bolter operator, where the average DGF 
was only 30%, i.e., a 70% reduction in visibility. 

Discomfort glare increases eye fatigue and pain, and 
causes distraction. The exact mechanism by which discom- 
fort glare causes pain is not known, but probably has some- 
thing to do with the muscles that constrict the pupil when 
faced with a bright light. Actually, the absolute intensity 
of the glare source is not important, but rather the dif- 
ference in contrast between the source and the general adap- 
tation level of the eye. A 200-W lightbulb would not cause 
discomfort glare, outside, on a sunny day; but it would on 
a dark moonless night. 

Because discomfort glare is a subjective experience, 
some people are more tolerant of discomfort glare, while 
others are more sensitive. For example, Whitehead (49) 
reported on sensitivity to discomfort glare among under- 
ground coal miners. The results showed that the miners 
were no more sensitive to discomfort glare than nonmin- 
ing populations. 



Trotter (44) listed the following ways to reduce glare in 
the mining industry: 

1. Avoid small sources of high luminance. The use of 
frosted tungsten-filament bulbs rather than clear bulbs, for 
example, increases the surface area of the source and thus 
reduces glare. 

2. Use large sources of low luminance. Fluorescent tubes 
provide larger, low-luminance sources. The veiling bright- 
ness effects of disability glare are the same whether the 
glare source is small and of high luminance, or large and 
of low luminance, provided that the illuminance at the eye 
is the same. The large, low-luminance source, however, will 
produce less discomfort. 

3. Move luminance sources out of the field of view. A 
source of light above the line of sight is less distracting than 
one that lies to the side or below it. As a rule of thumb, the 
angle between the horizontal line of sight and a line from 
the eye to the light source should be greater than 30°. 

4. Shield sources from direct view. As miners approach 
a shielded light source, they cannot see the source directly. 
When they are under the source, it no longer is in the field 
of view. 

5. Use prismatic lenses, filters, or cross polarizers. These 
devices diffuse the light from the source, effectively increas- 
ing its size and reducing its apparent brightness. 

6. Keep differences in luminance small between visible 
source and background. Use low-luminance sources in large 
surrounds or direct some of the light to illuminate the area 
beyond the source. 

7. Keep background and surround luminances high. The 
ratio of luminances of the task, the background, and the 
environment should not exceed 10:3:1, with a 10:5:2 ratio 
being very good. Generally, providing peripheral lighting 
yields acceptable ratios. 

8. Position work and lighting properly. A change in the 
angle of a light source or the position of the task relative 
to the position of the worker can reduce reflected glare. 

9. Avoid specular surfaces. This relates to reflected glare 
from shiny surfaces; use matte or rough surfaces instead. 

10. Use light of the right quality. Color of illumination, 
as for example the yellow of pressure sodium lamps, is 
believed to penetrate dust and fog better than white, green, 
or blue light. 



NOISE 

Since the advent of mechanized mining, noise has 
become an integral part of the mining environment. As 
equipment becomes more powerful, noise levels generally 
increase. Noise as an environmental factor has important 
implications for the worker population. The obvious implica- 
tion is, of course, the potential for noise-induced hearing 
loss. In addition, noise produces other health effects, in- 
fluences work performance, and makes communications 
more difficult. Noise is probably the most prevalent envi- 
ronmental stressor in the mining industry, considering both 
surface and underground operations. 

Measurement of Noise 

Noise, and sound in general, originates as vibrations. 
The two primary characteristics of sound are frequency and 
intensity. 



_ 



103 



Frequency 

Sound waves are really alternating increases and de- 
creases in air pressure caused by a vibrating source. Figure 
8-2 shows the waveform of a simple sound source. The wave 
is called a sinusoidal or sine wave. The height of the wave 
above the midline, at any point in time, represents the 
amount of above-normal air pressure at that point. Points 
below the line represent the below-normal air pressure. One 
complete cycle is shown in figure 8-2. The number of cycles 
generated per second is the frequency of the sound and is 
measured in hertz, which is equivalent to cycles per second. 
Complex sounds can be decomposed into an additive set of 
sine waves of various frequencies. 

Intensity 

The intensity of sound pressure level (SPL) of a sound 
is defined using a logarithmic measure called the decibel. 
It is really based on the ratio of two sounds, one of which 
is an arbitrary standard set to represent dB. The formula 
of SPL is as follows: 

SPL (dB) = 20 log Pj/P,, 

where P ; = the sound pressure (usually measured in 

^N/m 2 ) of the sound being measured 
and P r = 0-dB reference level (usually 20 juN/m 2 ). 

Notice that the 0-dB reference level cannot itself be zero 
because the Pj-P r ratio would be infinity. The reference 
level is set at an SPL roughly equivalent to the lowest in- 
tensity, 1,000 Hz pure tone, that a healthy adult can just 
barely hear under ideal conditions. Therefore, when the 
sound pressure of the sound being measured equals the 
reference level, the Pj-P r ratio equals 1.0, and the log of 
1.0 equals zero, hence dB. 

There are several implications of using the decibel scale: 
(1) sounds can have intensities less than dB; (2) a dou- 
bling of the power of a sound will increase the SPL by only 
3 dB; and (3) signal-to-noise ratios are really just the dif- 
ference between the SPL for noise and the SPL for signal. 

Indexes of Noise Intensity 

As discussed in chapter 3, the ear is not equally sen- 
sitive to all frequencies of sound; it is more sensitive to fre- 
quencies in the 2,000- to 6,000-Hz range, and less sensitive 
to lower frequencies. To account for this differential fre- 
quency sensitivity, sound pressure meters contain fre- 
quency-response weighting networks that electronically 
attenuate sounds of certain frequencies, and produce a 
weighted total sound pressure level. The networks are 
designated A, B, and C; and their relative responses, as 
given by Jensen (26), are shown in figure 8-3, along with 
the response characteristics of the ear at threshold. Of the 
three scales, the A scale comes closest to approximating the 
response characteristics of the ear. This scale is used by 
MSHA to set environmental noise criteria. 

Noise often varies in intensity over time. To account for 
this, a time-weighted average of the noise exposure can be 
computed. The Environmental Protection Agency recom- 
mends the equivalent sound level (LgJ as the best measure 
of the cumulative effects of noise. The equivalent sound 
level is defined as the sound pressure level (usually 
measured in decibels, A weighted) of a constant noise that, 



Above-normal 
air pressure 

Below-normal 
air pressure 




Corresponding changes 
in density of air molecules 

Figure 8-2. — Sine wave sound pressure wave showing one cy- 
cle with corresponding changes in air pressure. 



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(Courtesy of National Institute for Occupational Safety and Health) 



over the time period being measured, transmits to the 
receiver the same amount of acoustic energy as the actual 
time-varying sound. For example, if a person is exposed to 
100 dBA for 1 h and quiet for the next 4 h, the L eq for the 
total 5-h period would be 94 dBA. That is, 5 h of 94-dBA 
noise is equivalent in acoustic energy to 1 h of 100 dBA and 
4 h of quiet (less than 80 dBA). Sound pressure meters have 
been developed that give direct readouts of L eq values. 



Conditions in Mining 

Figure 8-4 presents an overview of the noise levels 
typically experienced in underground and surface mining 
by operators of various types of equipment (18). As can be 
seen, all the levels listed exceed 90 dBA. With the excep- 
tion of longwalls, underground shuttle cars, and surface 
trucks, all exceed 100 dBA. 



104 



Standards for Noise Exposure in Mining 

In the United States, the Walsh-Healy criteria for noise 
exposure, shown in table 8-3, are the standards set for 
underground and surface mining. Comparing these stand- 
ards against the typical levels reported in figure 8-4 makes 
it very likely that operators are exceeding recommended 
noise exposure criteria. For example, the noise exposure of 
over 700 underground coal miners was studied by Bobick 
and Giardino (8). They found that 20% of the miners were 
overexposed according to the Walsh-Healy criteria. 



Table 8-3.— Walsh-Healy noise criteria for underground 
and surface mining 

Max noise Max expo- 
level, dBA sure time, h 

90 •. .. 8 

92 6 

95 4 

97 3 

100 2 

102 1.5 

105 1 

110 .5 

115 .25 



Hearing Loss 

As would be expected, daily exposure to high levels of 
noise results in permanent hearing loss. The National In- 
stitute for Occupational Safety and Health (31 ) conducted 
a hearing survey of 1,500 underground coal miners who had 
no history of significant nonoccupational noise exposure, 
severe head trauma, or chronic ear infections, and had been 
out of the working environment for at least 14 h. Figure 
8-5 presents the results, showing the percentage of miners, 
by age, who suffered hearing loss of 25 and 40 dB for the 
frequencies of 1,000, 2,000, and 3,000 Hz (these are impor- 
tant frequencies for speech perception). By age 50, approx- 
imately half of the miners had a hearing loss in excess of 
25 dB, and about 30% had a loss exceeding 40 dB. These 
statistics were measurably worse than the national average. 

Other Physiological Effects of Noise 

Noise acts as a nonspecific physiological stressor. The 
onset of a loud, unexpected noise will cause a startled 
response. This usually involves flexion of the arms, arching 
of the torso, and blinking. Although not harmful, it may 
cause a person to be injured, or to injure others. Much of 
the literature dealing with the physiological effects of noise 
was reviewed by Antecaglia and Cohen (3). They reported 
the following noise effects noted by various researchers: 

1. Undue excitability and nervousness. 

2. Reduced speed of eye movements to focus clearly on 
objects. 

3. Narrowing of the visual field. 

4. Modification of the perception of color (partial deficiency 
for perceiving red). 

5. Increased secretions of corticosteroids (an indicator of 
general stress). 

6. Constriction of blood vessels, fluctuations in blood 
pressure, and cardiovascular irregularities. 

7. Increased gastric secretions. 




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Figure 8-4.— Typical noise levels of machinery in underground 

(A) and surface (B) mining (18). (Courtesy of US Mm Safety and Hearth 
Administration) 



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60 



70 



Figure 8-5. — Hearing loss among underground coal miners, by 

age (18). (Courtesy of U.S. Mine Safety and Hearth Administration) 



I 



105 



It must be emphasized that these changes are, for the 
most part, small. The long-range effect of continual noise 
exposure has not really been addressed outside the realm 
of hearing loss. There is some evidence of potential stress- 
related problems, but the reports are few and sketchy at 
best. 

Effects of Noise on Performance 

The effects of noise on performance depend heavily on 
the task being performed. The more cognitively demanding 
a task, the more likely it is that noise will adversely affect 
performance. Performance of simple, routine tasks shows 
little or no effect from noise, and in some cases even shows 
a facilitative effect. One effect of high noise is that people 
tend to funnel attention on a task, focusing on the most im- 
portant aspects and ignoring peripheral aspects. This may 
be fine for simple tasks, but where information may be com- 
ing from many sources and directions, funneling increases 
the probability of missing important information. 

One important detrimental effect of noise, of course, is 
that is masks auditory cues. If workers depend on sound 
cues : or voice communications to perform their jobs effi- 
ciently and safely, noise robs them of that valuable infor- 
mation, and safety and performance will suffer. 

Controlling the Noise Problem 

Noise can be controlled at the source, along the path 
from the source to the receiver (i.e., operator), and at the 
receiver's ear. In the mining industry, most efforts at noise 
control have been directed at reducing noise at the source 
and at the receiver. Little effort has been directed toward 
reducing noise along its path by using enclosures and bar- 
riers. Some processing plants have used sound absorption 
and acoustic enclosures to reduce ambient noise, but such 
approaches are less feasible when the sound source is 
mobile, such as a truck or drill (although treating the in- 
side of a truck cab with absorbent material is often used). 

Because sound is essentially caused by vibrating objects, 
the aim of noise reduction programs has been to reduce the 
vibrations of the machine or component generating the 
noise. The discussion of sound-reduction techniques is 
beyond the scope of this report. However, a few general prin- 
ciples of noise control are discussed and the results of a few 
noise-reduction programs in the mining industry are 
presented in this chapter. 

Low-frequency noise, the predominant type of noise in 
many mining situations, is attenuated less than high- 
frequency noise as it travels in air. In addition, low frequen- 
cies are much harder to contain using barriers and enclo- 
sures than are high frequencies because low frequencies 
travel over and around obstacles and through small holes. 
High frequencies, on the other hand, are more easily 
deflected. Although harder to contain, low frequencies are 
less harmful than high frequencies. 

When an object vibrates at its natural frequency related 
to its mass, it resonates. Resonance actually increases the 
amplitude of the vibration and, hence, the noise. This is 
dramatically demonstrated by wetting your finger and 
gently rubbing around the rim of a stemmed glass, caus- 
ing the glass to vibrate. By changing the speed and pressure 
of the rubbing action, the resonant frequency can be found, 
and the glass will emit a very loud tone. Be careful, 
however; the resonance can increase the vibration to the 
point of shattering the glass. 



In the context of noise control, a piece of equipment 
vibrating at its resonance frequency will emit loud noises. 
The noise can be reduced by changing the natural frequency 
of the equipment. For example, adding or removing mass 
(e.g., bolting a plate to the machine), drilling large diameter 
holes in very flat plates, or tightening loose bolts can reduce 
resonance. 

Because vibration causes noise, isolating the vibrating 
machine from surrounding structures also can reduce noise. 
Using vibration-isolation springs, pads, etc., for example, 
often drastically reduces noise. Such isolation materials, 
however, must be selected carefully because they could 
change the natural frequency of a machine and cause the 
equipment to resonate, thus actually enhancing the noise 
output of the source. 

Noise from fluids flowing through pipes is usually 
caused by turbulences in the flow. Such turbulences can be 
caused by abrupt pressure changes, such as opening and 
closing a valve quickly, or by sharp bends or partial obstruc- 
tions in the pipes that set turbulences in motion. Using 
fewer or softer (less than 90°) bends and not placing bends 
close together will often reduce flow-generated noise. 

Noise generated by fans can be reduced by changing the 
pitch and/or number of blades in the fan or by supplying 
an uninterrupted, nonturbulent flow of air to the fan. Posi- 
tioning a fan so that the intake side is close to corners or 
baffles will cause a turbulent flow of air to enter the fan 
and will increase noise. The purchase of a commercially 
available silencer from the fan manufacturer is probably 
the most cost-effective solution. 

The Bureau has published a handbook of noise control(5) 
that details specific noise control procedures for various 
types of surface, underground, and preparation plant equip- 
ment. Included are the noise characteristics of particular 
mining machines, noise-control treatments, anticipated 
reductions in noise level, cost, and commercially available 
sources for noise reducing kits, components, etc., references, 
and case history reports. As an example, figure 8-6 presents 
a page from this handbook for diesel-powered rotary drills 
used in surface mining. 

A project to reduce noise exposure to operators of diesel- 
powered track dozers was discussed by Daniel (13). One 
dozer had no operator cab and only a rollover protective 
structure (ROPS). The noise level at the operator's ear was 
105.5 dBA. Through the series of modifications listed in 
table 8-4, the overall noise level was reduced 11.5 dBA, to 



Table 8-4.— Effects of noise control treatments installed 

on a diesel track dozer equipped with ROPS only (13), 

decibels (A-weighted) 





Sound 


Reduction from 


Treatment 


level 


baseline 


None (baseline) 


105.5 


NAp 
4 


Windshield 


101.5 


Absorption under ROPS 


102.5 


3 


Exhaust muffler 


104.0 
100.0 


1.5 


Windshield and absorption 


5.5 


Windshield, absorption, and muffler 


99.5 


6 


Windshield, absorption, muffler, and dash 






seals and isolation 


96.5 


9 


Windshield, absorption, muffler, dash seals 






and isolation, and floor seals 


95.5 


10 


Windshield, absorption, muffler, dash seals 






and isolation, floor seals, and seat seals . . . 


95.0 


10.5 


Windshield, absorption, muffler, dash seals 






and isolation, floor seals, seat seals, tank 






seal, and hydraulic valve cover 


94.0 


11.5 



NAp Not applicable. 



106 



DIESEL-POWERED ROTARY DRILLS 




Owse< E*hau« {(( 



Typical noise level 
85-100 dBA 



II) Hydraulic Ncise 



Treatment 



Quieted 

noise 

level, dBA 



Cost and 
labor 



Status 



Refer- 
ence 




Add mufflers(s) 
to engine 
exhaust 



85-95 S100-S450 Commercially available Al 

2 h for all models. C2 




Modify existing 
cab. 



75-90 $500-$900 
20-80 h 



Local design and 
fabrication required. 



Ill 



A4 
Bl 
B2 




Add acoustic 
cab. 



70-85 $10,000$ 15.000 Commercially available 
80-140 h for some models. 



A2 
A4 
B2 



n 



Add enclosure for 
engine with 
mufflers. 



75-90 $1.500-$8.000 
140-280 h 



Local design and B2 

fabrication required. B4 




Add partial barrier 
at operator with 
mufflers. 



80-95 $500-$2.000 
20-120 h 



Local design and 
fabrication required. 



A4 
Bl 
B2 



6. 




Modify cooling fan 
with mufflers 
for models with 
noisy fans. 



85-95 



$500-$2,000 
20-120 h 



Local design and 
fabrication required. 



B3 



7. 



^ 



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with covers for 
hydraulic valves, 
dust collector for 
blow air, and 
isolated cen- 
tralizer or drill 
pipe snubber. 



80-90 



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200-250 h 



Local design and 
fabrication required. 



A3 
A4 
Bl 
B2 
B3 



Recommendation* 

Reduce engine noise using a muffler, cab, or barrier 
as appropriate. 



Acoustically treated noise level 
75-90 dBA 



Figure 8-6.— Example of type of information contained in Mining Machinery Noise Control Guidelines (5). 



107 



94 dBA. This represents a one-sixteenth reduction in sound 
power, and a one-half reduction in loudness. About 6 dBA 
of reduction was obtained by providing a windshield, muf- 
fler, and sound-absorption material under the ROPS canopy. 
The remaining 5.5-dBA reduction resulted from carefully 
sealing openings and isolating the dash from engine 
vibrations. 

As a final example, a Bureau project to reduce noise 
levels in low-seam, underground coal mine, mantrip trolley 
cars was reported on by Galaitsis and Bobick (17). Noise 
levels were typically 90 to 100 dBA in such vehicles at nor- 
mal operating speeds. The major noise sources were the 
wheel-rail interface system and the drive motor and train. 
The noise-reduction treatments included metal panel damp- 
ing, soft spring seats, soft suspension arm bushings, suspen- 
sion arm guideplate isolators, motor enclosures, motor 
mounts, and helical gears. Figure 8-7 shows the results of 
the treatment for the passenger and operator compartments, 
with average reductions of 5 to 10 dBA obtained. (Note that 
a decrease of 3 dB represents a reduction of sound power 
by one-half.) 

Hearing Protection 

If noise cannot be reduced at the source or in its path, 
then hearing protection should be worn by the exposed 
worker to reduce the noise level reaching the vulnerable 
structures of the inner ear. There are a wide variety of hear- 
ing protectors available: earplugs, muffs, custom ear molds, 
etc. The two most common types are insert-type and muff- 
type protectors. Table 8-5 presents the advantages and 
disadvantages of each (37). 



Table 8-5.— Advantages and disadvantages of insert-type 
and muff-type hearing protection devices (37) 

Courtesy of Charles C. Thomas, Publisher, Springfield, IL 
MUFF 

Advantages More attenuation and less variable. 

Single size. 

Easily monitored for wearing compliance. 

Usually more comfortable. 

Persons with infected ears can wear them. 

Harder to lose. 
Disadvantages Uncomfortable in heat. 

Harder to store or carry. 

Suspension forces may decrease with bending, 
and attenuation may vary. 

Large size. 

Expensive. 



INSERT 
Advantages .... 



Small size. 

Easily worn with other headgear. 
Comfortable in hot environments. 
Inexpensive. 

Disadvantages More fitting time required. 

Less attenuation and more variable. 
Dirt may be inserted into the ear canal with 
the plug. 

Hard to monitor for wearing compliance. 
Only persons with healthy ears can wear them. 



Each type and make of hearing protection has slightly 
different attenuation properties. Some give better attenua- 
tion at lower frequencies, some at higher frequencies. It is 
important, therefore, to select hearing protection that 
matches the environmental noise characteristics for which 
protection is sought. It must be pointed out, however, that 
the attenuation curves published by manufacturers are usu- 
ally generated under more or less ideal laboratory condi- 



< 



100 



90 



80 



E A 



i A ^ Untreated 



UJ 

> 70 
UJ 
I 100 



3 

O an 

V) 90 



80 



70 



^j\AvV\ 




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Treated ^ 

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vvr v : 



10 



20 

TIME, s 



30 



40 



Figure 8-7.— Typical noise-time histories in passenger and 
operator compartments of an untreated and noise-reduction- 
treated mantrip (17). 



tions. These data do not take into account wearing habits, 
fit, interference with safety glasses or hair, and other on- 
the-job factors. For example, tests conducted with muff-style 
protectors in the underground environment were reported 
on by Nguyen (32). Whereas the manufacturer claimed at- 
tenuation of 25 to 30 dBA, actual measurements showed 
values of 10 to 16 dBA. In other tests, it was found that 
suspension fatigue and cushion deterioration had only a 
minor effect on attenuation, but leakage caused by safety 
glass temples resulted in up to a 5-dBA loss in attenuation. 
Insert-type protectors, if properly inserted, are not affected 
by interference of eyeglass temples and hair, as are muff- 
type protectors. 

An objection often given by workers to wearing protec- 
tion devices is that such devices reduce speech intelligibility 
and make it more difficult to hear warnings and other aud- 
itory signals. The evidence, however, indicates that wear- 
ing hearing protection does not necessarily reduce speech 
intelligibility. In high noise level conditions, above 80 dBA, 
wearing hearing protectors reduces both noise and speech, 
and brings them into a range where they can be more eas- 
ily discriminated, hence, increasing intelligibility. The prob- 
lem is that when people wear hearing protectors, they tend 
to speak more softly than when not wearing them. Person- 
nel have learned to change their voice levels to compensate 
for a noisy environment, and the quieting effect of hearing 
protectors cause the wearers to tbink it is quieter than it 
really is. The upshot is that people must be instructed to 
speak loudly, slowly, and distinctly in noisy environments 
and to be cognizant of the effect of hearing protectors on 
their speech intensity. Thus, hearing protection per se does 
not decrease intelligibility for a listener, but it may reduce 
the speaker's intensity. 

Tbere is some evidence that wearing hearing protection 
can reduce the ability to localize sounds. Approximately 
50% more errors in sound localization were found by 



108 



Atherley and Noble (4) when subjects were wearing protec- 
tion. There was also a marked increase in left-right errors, 
where the subjects reported a sound on the right as coming 
from the left, or vice versa. 

Hearing protection should not be considered a perma- 
nent solution to a noise problem, but rather only a tem- 
porary fix while efforts are being made to reduce the noise 
level at the source or along its path. 



WHOLE-BODY VIBRATION 

Whole-body vibration is prevalent in both surface and 
underground mining environments. In surface mining, 
mobile equipment operators are exposed to vibration and 
buffeting as they drive their vehicles over bumpy roads. In 
underground mining, shuttle car and scoop operators, as 
well as miners being transported by mantrip, are also ex- 
posed to vibration and buffeting. Vibration was discussed 
in chapter 6 in the context of handtools. Although handtool- 
induced vibration, as any jackleg drill operator will confirm, 
can shake your entire body, it is necessary to distinguish 
that sort of vibration from the lower frequency, higher 
amplitude vibration transmitted to the whole body by 
mobile equipment. The physiological and performance ef- 
fects of the two types of vibration are somewhat different. 



Vibration Terminology 

Vibration is primarily of two types, sinusoidal and ran- 
dom. As was discussed in relation to noise, sinusoidal mo- 
tion is regular and repeats itself at set intervals. Most 
studies of the effects of vibration on humans use sinusoidal 
wave patterns. Random vibration, as would be expected, is 
irregular and unpredictable; most real-world vibration is 
random. 

Vibration occurs in different directional planes (up- 
down, forward-backward, left-right), with the predominant 
vibratory forces experienced in the mining environment in 
the up-down plane. 

As in the case of noise, whole-body vibration is discussed 
in terms of frequency and intensity. In the case of sinusoidal 
vibration, frequency is defined in hertz, and intensity is 
defined in several ways: amplitude (measured in inches or 
feet); displacement (inches or feet); velocity (inches or feet 
per second); or acceleration (inches or feet per square sec- 
ond). Sometimes acceleration is expressed in terms of 
number of gravity (g) where 1 g = 386 in/s 2 or 32.17 ft/s 2 . 

The situation becomes more complex with random vibra- 
tion, because the frequency spectrum varies randomly. Fre- 
quency is usually displayed in a power spectral-density plot, 
showing the power density (gravity squared per hertz) in 
each frequency band. Intensity is often expressed as root- 
mean-square acceleration (e.g., RMS G) and is a measure 
of the total energy across the frequency range. 

Vibration transmitted to the body can be amplified or 
attenuated as a consequence of body posture (e.g., standing, 
sitting), muscle activity (e.g., relaxed or rigid), type of 
seating, and the frequency of the vibration. Every object 
has a resonant frequency related to its mass. When an ob- 
ject is vibrated at its resonant frequency, the object will 
vibrate at maximum amplitude, greater than the amplitude 
of the original vibration. This is called resonance. Different 
parts of the body have different resonant frequencies. The 
following is a partial list of frequencies, in hertz: Vertebras 



of neck and lumbar region, 2.5 to 5; trunk, shoulder, and 
neck, 4 to 6; head and shoulders, 20 to 30; and eyeballs, 60 
to 90. 

It is generally agreed that frequencies between 4 and 
8 Hz are most likely to cause damage to the back and spine 
because of resonance of these body parts. 



Effects of Vibration on Humans 

The effects of vibration on humans can be divided into 
two classes, health effects and performance effects. 

Health Effects 

Several studies have been conducted on individuals ex- 
posed to whole-body vibration on the job: tractor drivers, 
truck drivers, bus drivers, and heavy equipment operators. 
All the studies suggest that low-frequency vehicle vibra- 
tions are associated with increased incidence of lower-back 
pain, disk and vertebra degeneration, gastrointestinal dis- 
orders, and hemorrhoids. The problem is that not all of these 
ailments can be attributed to vibrations alone; it is likely 
that other factors, such as maintaining a fixed-seated 
posture, irregular and poor eating habits, and physical lift- 
ing associated with the job, may have contributed to some 
of these disorders. It was reported by Cain and Pettry (10) 
that at one coal company in 1983, 33^ of back injuries oc- 
curred to persons employed in jobs where they were regu- 
larly exposed to whole-body vibration, yet only 20^ of the 
workforce were in such jobs. 

Performance Effects 

The primary performance effects of vibration are on 
visual and manual tasks. Decrements in visual acuity oc- 
cur most prominently with vibrations in the 10- to 30-Hz 
region. Vibration does not seem to have much of an effect 
on cognitive performance or speed-of-reaction time. Vibra- 
tion leads to fatigue, partly because it causes muscles to 
tense in order to steady the body or attenuate the vibra- 
tion. This general fatigue can, of course, lead to reduced 
cognitive-processing capability. It was reported by Grand- 
jean (21) that vibration impairs driving efficiency and in- 
creases errors, which may result in accidents. 



Vibration Exposure Standards 

Researchers have for years been trying to develop a 
standard for human exposure to whole-body vibration. In 
1974, the International Organization for Standardization 
published a recommended exposure standard for % - ertical 
and lateral vibration (24). Three criteria were established: 
fatigue-decreased proficiency boundary (FDPl beyond which 
working efficiency was postulated to decrease: health ex- 
posure limit, which is equal to two times the FDP; and the 
reduced comfort boundary tRCB). equal to FDP 3.15. Figure 
8-8 shows the FDP criteria for vertical vibration. Curves 
are shown for 8-h, 1-h. and 1- to 4-min exposures. The 
criteria, although widely accepted, can only be considered 
approximate. Evidence has accumulated that challenges the 
validity of the criteria (48). and that indicates that fatigue 
effects occur at lower levels and for shorter durations than 
the criteria suggest. 



109 



100 



N 

< 10 



z 
o 

g 

QL 
hi 

_i 
til 
o 

S 1.0 



: 


i i i 1 1 1 1 1 1 i i i 1 1 


1 1. 


- 


At any t point, health limit = 2 X FDP 
Comfort limit = FDP/ 3.15 


' - 


— 




\ 


; 


"N. 1-4 min/ / 




-^ 


^\. 1h / / 


- 


- 




" 


- 


^\. 8h X 


- 




i i i i i i 1 1 1 i i i i i 


i i 



250 



10 



100 



FREQUENCY, Hz 



Figure 8-8.— Vertical vibration exposure limits for preservation 
of performance (fatigue-decreased proficiency, FDP) (24). 

(Copyright 1974 by the American National Standards Institute Inc., and reprinted with 
permission) 



m 

2 



i I «" 

KEY 
--- Contoured chair 

— Standard driver's 
seat 

•— •• Suspension seat 




160-lb man, normal \ 
sitting position, accel- \ 
eration measured at 
belt 



J. 



2 4 6 

FREQUENCY, Hz 

Figure 8-9.— Mechanical response of a person's body to vibra- 
tions when sitting in different seats (39). 



Vibration Exposure of Surface Coal Miners 

The vibration exposure of surface coal miners operating 
equipment such as track dozers, scrapers, haulers, blasthole 
drills, motor graders, and shovels was measured by Rem- 
ington (36). This work indicated that about half of all sur- 
face machine operators are exposed to vibration exceeding 
the FDP criteria; only about 15% experience vibration ex- 
ceeding the health exposure limit. The machines in which 
operators were most likely to exceed the FDP criteria (prob- 
ability = 0.87-0.90) were scrapers, dozers, and loaders. 
Truck drivers were next most likely (probability = 
0.56-0.58), followed by grader operators (probability = 0.32). 
The operators of blasthole drills, shovels, and draglines were 
exposed to very little vibration. Remington concluded that 
although one would not expect to see many mine machine 
operators with vibration-induced health effects, one would 
expect to find significant numbers with impaired ability to 
operate their machines safely and efficiently because of 
vibration exposure. 

Controlling Vibration 

Vibration can be reduced at the source through engi- 
neering modifications to the equipment, including better 
suspension systems and component isolation. In addition, 
shock-resistant seats can be installed to reduce the inten- 
sity of the vibration reaching the operator's body. Figure 
8-9 shows the transmission of vibration to a seated person 



in three types of seats (39). As can be seen, the suspension 
seat reduced the level of vibration considerably. The amp- 
litude of vibration was actually increased when the person 
sat in the contoured and standard seats. The cost of a good 
pneumatic seat can accrue dividends in increased worker 
health, comfort, and efficiency. 



HEAT STRESS 

Thermal conditions in mining run the gamut from bit- 
ter cold, experienced by surface miners in the winter, to hot 
humid conditions, experienced in deep underground mines. 
Heat stress is probably more prevalent, and certainly more 
dangerous, than cold stress. The body can tolerate cold 
stress much better than heat stress, and the performance 
effects of cold stress seem to be more restricted than is the 
case with heat stress. 

Physiological Response to Heat Stress 

As discussed in chapter 7, the body oxidizes glucose t» 
release energy and heat. The more physically demanding 
an activity, the greater the amount of heat generated. This 
is the process of metabolism, and it can increase heat pro- 
duction 10 to 20 times greater than at rest. The body also 
gains and loses heat from and to the environment. Heat is 
gained or lost due to convection (the mixing of cool and 
warm air and the transfer of heat by molecular contact of 



110 



the air molecules), conduction (direct contact with another 
object— usually so negligible that it is combined with con- 
vection), and radiation (the transfer of heat by electro- 
magnetic radiation— as is done by the sun or hot object not 
in direct contact with the body). The body loses heat through 
evaporation (the conversion of water to water vapor). Evap- 
oration is the principal avenue of heat loss for the body, and 
is regulated by producing sweat and diverting heated blood 
to the skin for evaporative cooling. 

The body attempts to maintain a state of internal ther- 
mal equilibrium. That is, the body regulates blood flow and 
sweat production to maintain a constant (or nearly constant) 
core temperature. Core temperature is the temperature of 
the deep body organs and is approximated by rectal 
temperature. As the body gains heat, due to either increased 
metabolism or by exposure to a hot environment, the heart 
beats faster and pumps more blood with each beat (i.e., in- 
creased cardiac output). In addition, the blood vessels in the 
skin dilate to allow the heated blood from the core to flow 
to the skin and to be cooled, especially by evaporation. 

In addition to the cardiovascular response to heat stress, 
the body produces sweat that keeps the skin moist and is 
the principal medium for evaporative cooling. If the body 
can dissipate the metabolic and environmental heat build- 
up, no major problems occur. If not, serious physiological 
consequences, including death, can ensue. 

Excessive heat stress leads to heat cramps, heat exhaus- 
tion, and heat stroke. Heat cramps are painful muscle 
cramps caused by excessive sweat loss. The cramping can 
occur during or after work, and usually affects those muscles 
most involved in the work. 

Heat exhaustion is caused by excessive loss of water. 
The worker with heat exhaustion experiences dizziness, ex- 
treme weakness or fatigue, nausea, and headaches. Heat 
stroke is the most serious health problem and can often lead 
to death. Basically, in heat stroke, the body's heat dissipa- 
tion system cannot cope with the heat stress placed on it. 
Either the sweat glands fatigue and cease producing sweat, 
or the system simply cannot adequately dissipate the heat 
load. Core temperature rises and the hot blood damages the 
vasomotor control centers in the brain; liver and heart 
damage can also occur. Blood vessels dilate and insufficient 
blood is returned to the brain and heart, and the person 
often will go into shock. Immediate medical attention is re- 
quired to prevent death. 

Figure 8-10, based on work by Bell (7), shows the 
number of minutes unacclimatized workers can tolerate 
various combinations of dry bulb temperature and relative 
humidity. The data were generated by young, fit men step- 
ping on and off a stepstool, 12 times per minute. The men 
continued the activity until exhausted. As shown, at these 
relatively high temperatures and this work rate, collapse 
occurred in less than 2 h. 



158 



140 



UJ 

cc 

3 

a: 

UJ 

Q. 

UJ 

r- 



122 



104 



86 



.30 % relative 
humidity 




i. 



20 40 60 80 100 

COLLAPSE TIME, min 



120 



Figure 8-10. — Time until young, fit, unacclimatized men col- 
lapse from exhaustion caused by stepping on and off a stepstool 
12 times per minute. (Adapted by Bell (7) from reference 33.) 

(Copyright 1982 by John Wiley and Sons, and reprinted by permission) 



indexes have been universally accepted because each has 
its own shortcomings. Despite this, a few indexes seem to 
have acceptability, and several exposure limit standards 
are based on them. Three of these indexes— effective tem- 
perature, wet-bulb-globe temperature, and Belding-Hatch 
heat stress index— are discussed in the following sections. 
Jensen (27) compared these heat stress indexes and 
found very high correlations between wet-bulb-globe tem- 
perature and corrected effective temperature, but lower cor- 
relations between these measures and the Belding-Hatch 
heat stress index. Similar results have been reported by 
Morris (30). 



Effective Temperature (ET) 



Indexes of Heat Stress 

Heat stress is the total neat load on an individual from 
environmental and metabolic sources. Heat stress is distin- 
guished from heat strain, which is the biochemical, physi- 
ological, and psychological adjustments made by an 
individual in response to the stress (27). 

Over the years, many attempts have been made to 
develop indexes of heat stress by combining several envi- 
ronmental and task variables into a single number to repre- 
sent the heat load on an individual. None of a dozen or more 



ET is an index of the warmth felt by the human body 
on exposure to various combinations of air temperature, 
humidity, and air velocity, using as a reference the tem- 
perature of an environment with still, fully saturated (100*5 
relative humidity) air. Thus, if a given combination of tem- 
perature, humidity, and air velocity yields an ET of 85 c F. 
that environment would give the same thermal sensations 
as an environment of 85 " F, 100*5- relative humidity, and 
no air velocity. As pointed out by Jensen (27). ET does not 
include the effects of radiant heat (e.g.. the sun\ and hence 
underestimates heat load in environments where radiant 



Ill 



heat exists. Several investigations have proposed correc- 
tions to ET to take into account the effects of radiant heat. 
Another development in the ET index has been to relate 
the environments to 50%, rather than 100%, relative humid- 
ity, and to use equivalent skin wetness rather than ther- 
mal warmth felt. This scale is called corrective effective 
temperature (16). 

Wet-Bulb-Globe Temperature (WBGT) 

WBGT combines natural wet bulb temperature (NWB), 
globe temperature (GT), and dry bulb temperature (DB) into 
a single index using the following formula: 

Indoor application-WBGT = 0.3 GT + 0.7 NWB, and 
outdoor application-WBGT = 0.2 GT + 0.7 NWB + 0.1 
DB. 

Natural wet bulb temperature is obtained by wrapping 
the end of a thermometer with wet gauze. This simulates 
the evaporative cooling capacity of the environment, tak- 
ing into account the air movement and relative humidity 
in one measure. Globe temperature is obtained by placing 
a thermometer inside a copper sphere that is painted black. 
This measures the radiative heat load of the environment. 
Dry bulb temperature is simply the temperature reading 
from a dry thermometer suspended in the air. Figure 8-11 
shows a typical manual setup for obtaining the temperature 
readings necessary to compute WBGT. As will be seen, 
WBGT is fast becoming the measure upon which exposure 
standards are being based. There are electronic instruments 
available that display WBGT directly, but they are expen- 
sive. A simplified measure proposed by Botsford (9), called 
the wet globe temperature (WGT), consists of a dial ther- 
mometer with a heat sensor enclosed in a small copper 
sphere, covered with a wet black cloth (a Botsball). It is 
designed to take into account all the forms of heat exchange 
that affect a person's response to a hot environment, i.e., 
evaporation, conduction, convection, and radiation. 



Wet bulb 
thermometer 



l4 in 




Dry bulb 
thermometer 



Globe 
thermometer 



6-in copper ball 
*3mjtm ft P-'* d b '°' k 



Adjustable 
tripod 



Figure 8-1 1 .—Setup for manually obtaining temperatures used 
to compute wet-bulb-globe temperature. 



Heat Stress Index (HSI) 

HSI was developed by Belding and Hatch (6). It is one 
of the most comprehensive indexes available, but requires 
many measurements and uses a relatively complex formula. 
Basically, HSI is the ratio of the body's heat load from 
metabolism, convection, and radiation to the evaporative 
cooling capacity of the environment. The idea is that the 
heat load from these sources must be dissipated through 
evaporation. The ratio of heat load to evaporative cooling 
capacity of the environment therefore indicates the relative 
ease by which that heat load is dissipated. The index takes 
into account environmental factors, such as temperature, 
humidity, and air movement, but also includes metabolic 
rate and clothing effects. 

Heat Stress Conditions in Mining 

For the most part, heat stresses in undergound mines 
with adequate ventilation are not excessive. The major prob- 
lem encountered in underground mining is high humidity, 
which reduces the body's capacity to dissipate heat by 
evaporation. Crooks (11) surveyed underground metal- 
nonmetal worksites in the United States and found the dry 
bulb temperature averaged 62 ° F and ranged from 37 ° to 
79° F. Relative humidities, however, averaged 70%, and 
ranged from 13% to 99%. Over 25% of the worksites meas- 
ured had relative humidities over 90%. The warmer, more 
humid, and slower airflows were found in production and 
development sites, where the heaviest physical labor occurs. 
It is in such sites that heat strain becomes excessive if 
precautions are not taken. 

The wet bulb temperature in South African gold mines 
(much deeper than U.S. mines) was reported on by Van der 
Walt (46). Average temperature has been increasing for the 
last 20 yr, probably because of mining at even greater 
depths. It was estimated that half the total underground 
workforce in South African gold mines works in areas where 
the wet bulb temperature is above 86 ° F. This corresponds 
to a dry bulb temperature of 88 ° F and 90% relative humid- 
ity, or 92° F and 80% relative humidity. It is no wonder 
that from 1969 to 1980, 205 heat stroke accidents were 
recorded in South African gold mines, with 39 resulting in 
fatalities. 

Performance Effects of Heat Stress 

There are several specific effects of heat stress that 
reduce a worker's capability to perform efficiently and 
safely. Excessive heat reduces a person's capacity to per- 
form physically demanding work. In addition, the physically 
demanding work increases the overall heat stress placed 
on the individual. This results in reduced work output. The 
performance of miners loading mine cars and of drilling rock 
as a function of ambient temperature was reported on by 
Misaqi (29). The results, presented in figure 8-12, show that 
as temperature increased, performance declined rapidly. 

Heat stress also reduces one's ability to remain alert 
during lengthy and monotonous tasks, and reduces the 
ability to make quick decisions. In addition, heat stress can 
also, at times, contribute to frustration, anger, and other 
emotions. These effects, combined with slippery sweaty 
palms, dizziness, and fogging of safety glasses, can lead to 
higher accident rates in heat stress environments. For ex- 
ample, an investigation of the incidence of unsafe behaviors 
in a variety of industries as a function of WBGT was 



112 



reported on by Ramsey (34). The results, shown in figure 
8-13, indicate a U-shaped relationship, with the least inci- 
dence of unsafe behavior occurring between 62.6° F and 
73.4° F WBGT. Above or below this optimum range, unsafe 
behaviors increased. The effect was most pronounced for jobs 
requiring moderate workloads, which represent most min- 
ing jobs. It is usually the case that reducing heat stress can 
pay off for everyone: reducing physiological stress on the 
workers, increasing productivity, and reducing accidents. 



100 



80- 



tf 60- 



*: 
rr 
o 

5 



40- 



20 



- 


X ' X ' 


i i 


- 


_ 




V .Rock drilling 


- 


- 


Loading mine^^. 
cars-^ 




- 


- 


i i 


i i 


- 



78 



83 88 93 98 

AMBIENT TEMPERATURE, ° F 



103 



Figure 8-12.— Effects of ambient temperature on miners 
loading mine cars and drilling rock (29). (Courtesy ot us Mine safety 

and Health Administration) 



How Much Is Too Much 

The National Institute for Occupational Safety and 
Health (NIOSH), as discussed by Dukes-Dobos (14), has pro- 
posed exposure limits based on the WBGT. These are simi- 
lar to recommendations that have been accepted by the 
American Conference of Governmental Industrial Hygien- 
ists (1), the American Industrial Hygiene Association (2), 
and the International Organization for Standardization (25). 
Table 8-6 compares these standards for 8-h exposures at 
various levels of workload. It should be pointed out that the 
corrections for high-velocity airflow have been challenged 
by some investigators as not necessary (22). The various 
standards are very much in agreement, although the desig- 
nations of light, moderate, and heavy workload differ 
markedly. 

Table 8-6.— Comparison of proposed 
WBGT threshold values (35) 

(Reprinted with permission by Taylor and Francis, Ltd) 





Resting 


Light 


Moderate 


Heavy 


Very heavy 


ACGIH: 












Temperature . . °F . . 


NP 


86 


80 


NP 


77 


Energy . . . kcal/h . 


NP 


100-200 


201-350 


NP 


350-500 


AIHA: 












Temperature. . °F. . 


90 


86 


80 


NP 


NP 


Energy . . . kcal/h . . 


100 


200 


300 


NP 


NP 


OSHA: 












Temperature. . °F. . 


NP 


'86, 2 90 


'82. 287 


'79, 284 


NP 


Energy . . . kcal/h . . 


NP 


<200 


201-300 


>301 


NP 


ISO: 












Temperature . . °F . . 


91 


86 


82 


'77, 279 


'73. 2 77 


Energy . . kcal/h . . 


<100 


100-201 


201-310 


310-403 


>403 



ACGIH American Conference of Governmental Industrial Hygienists. 

AHIA American Industrial Hygiene Association. 

NP Nothing proposed. 

OSHA Occupational Safety and Health Administration. 

ISO International Organization for Standardization. 

1 Low-velocity ventilation. 

2 High-velocity ventilation. 



1.0 



V) 

o 



.8 



\ 



\ — 



KEY 

Heavy workload 
Moderate workload 
- — - Light workload 




41 50 59 68 77 86 
TEMPERATURE (WBGT), °F 



95 



Figure 8-13.— Relationship between rate of unsafe behaviors 
and wet-bulb-globe temperature (34). 



Standards are also available for intermittent work in 
a hot environment. These, however, diverge markedly, ac- 
cording to Henschel (22), because there are very few data 
available to provide guidelines. The relative physiological 
impact of short and long heat exposures is not known, nor 
is the extent of the effect of the rest area temperature on 
strain or if short rest and short work periods result in the 
same strain as long rest and long work periods. However, 
if the continuous work recommended exposure levels are 
adhered to, even for intermittent work, one would be confi- 
dent of erring on the side of safety. 

Protection From Heat Stress 

A number of measures can be taken to protect workers 
from heat stress. At a minimum, workers exposed to hot 
environments should be given specific training in the symp- 
toms and mechanism of heat stress, and how to protect 
themselves against heat stress. Work done in hot environ- 
ments can often be redesigned to reduce physical activity 
and hard labor. Work should be mechanized where possi- 
ble and paced to give frequent rest periods, and the overall 
exposure time to heat should be minimized. Heavy physical 
work in surface mining can often be scheduled for cooler 
times of the day. Cool rest areas should also be provided 
to maximize the benefits of rest. 



113 



Workers must be supplied with fresh drinking water 
and encouraged to drink, even if they are not thirsty. As 
it turns out, thirst is not a good indicator of dehydration. 
Water must be replenished on a regular basis, in quantities 
that match the sweat loss incurred. If the workers eat nor- 
mal meals and snacks, salt need not be added to the drink- 
ing water, nor should salt tablets be used. The use of salt 
in hot environments has a long history, but current evidence 
strongly discourages this practice. Ingestion of salt actually 
retards the acclimatization process, leads to high blood 
pressure, and does not mitigate the negative effects of heat 
stress (41). Recommendations by the American College of 
Sports Medicine suggest that fluid loss should be replaced 
with water having a 2.5% glucose (sugar) content. The tem- 
perature of the replacement water should be 45° to 55° F. 

Workers should be specifically selected to work in hot 
environments; the following characteristics among workers 
increase the likelihood of experiencing heat stress in hot 
environments: 

1. The taking of alcoholic drinks or narcotic drugs. 

2. The taking of antihistamines or diuretic drugs. 

3. Cardiovascular diseases. 

4. Sickness, especially if vomiting and diarrhea are 
symptoms. 

5. Body weight less than 110 lb (47). 

6. Over 45 yr of age (41). 

7. Poor physical condition. 

The work area should be redesigned, if feasible, to in- 
crease airflow by installing fans, ventilation tubes, or air 
conditioning. To shade surface workers from the sun, tent 
covers can be erected. 

Proper clothing should be insisted upon. On hot sunny 
days, lightweight cotton shirts and pants reduce the radiant 
heat load, and facilitate evaporation by soaking up sweat 
and bringing it to the surface. Head covering is important 
outdoors. Clothing should be loose fitting and not interfere 
with evaporative heat loss. Under extreme conditions, ice 
jackets can be worn to increase tolerance to heat stress (42). 

Probably the most promising approach to reducing the 
ill effects of heat stress is to institute a systematic accli- 
matization program for those who must work in hot envi- 
ronments. The Republic of South Africa has been a leader 
in developing and testing various methods for efficiently 
and safely acclimatizing workers and identifying those who 
are at high risk (38, 41 , 43). Acclimatization is required for 
workers who have to work in wet bulb temperatures of 82 ° 
F or above. In South African mines, 0.25 million men must 
undergo acclimatization each year. The acclimatization pro- 
cedure involves several components: (1) climatic room ac- 
climatization; (2) ascorbic acid (vitamin C) supplements; (3) 
microclimate suits; and (4) heat tolerance testing. 

The climatic room acclimatization involves working for 
4 h/d at a metabolic load that is increased progressively from 
150 kcal/(m 2 /h) on the first day to 240 kcal/(m 2 /h) on the 
eighth day. The climatic room is controlled at 89 ° F wet 
bulb. Workers are monitored for abnormal reactions and 
given treatment if needed. Strydom (41) found that this pro- 
cedure reduced the acclimatization period from 12 to 8 days, 
and required only 4 h/d as against full shifts. 

Workers are also given 250 mg of vitamin C per day, 
starting before acclimatization and continuing throughout 
the process. Results showed that acclimatization time was 
reduced from 8 to 4 days; and, in addition, fewer men were 
found to be heat intolerant. Without vitamin C, 3% to 5% 
of the men could not acclimate; with vitamin C, less than 
1% could not be acclimated. 



Use of ice jackets (microclimate suits) was found to 
reduce the ill effects of heat stress without retarding ac- 
climatization. Results showed that workers would become 
acclimatized to heat while doing their normal underground 
tasks wearing an ice jacket for 6 days. Finally, a procedure 
for screening workers to identify those who do not need ac- 
climatization (the hyper-heat-tolerants) and those who 
would not respond to acclimatization has been developed. 

In South African mines, despite increased average work- 
ing temperatures (due to mining at increased depths), 
Strydom (41) found that heat stroke cases have steadily 
declined over the last 20 yr, due in great part to the 
widespread use of systematic acclimatization procedures. 



COLD STRESS 

As the ambient temperature declines, the body takes 
defensive actions to maintain its thermal balance. The first 
defense is to constrict the blood vessels in the skin and ex- 
tremities, thereby keeping the warm core blood away from 
the cold surface. A second defense is shivering^hich serves 
to increase metabolic heat production and hence reduce or 
halt overall heat loss. Excessive fluid loss can also occur 
in cold environments, and cold-induced dehydration may 
persist for several days. 

The body can tolerate more cold stress than heat stress. 
Deep-body temperature can decline to 78° F before death 
occurs. There have even been cases of people (usually 
children) who have survived bodv cooling to 60 ° F if the 
drop occurred rapidly. 

Whereas there are a host of competing indexes of heat 
stress, there is really only one index of cold stress: windchill 
index (or temperature). Table 8-7 presents the temperature 
equivalent of various combinations of local temperature and 
wind speed as given by Siple and Passel (40). 



Table 8-7.— Equivalent temperatures based on windchill 
index (40), degrees Fahrenheit 

(Reprinted with permission by American Philosophical Society) 



Air temp °F. 

Calm 

5-mph wind 

10-mph wind 

20-mph wind 

30-mph wind 

40-mph wind 



40 



40 
37 
28 
18 
13 
10 



20 



20 

16 

4 

-10 

-18 

-21 



10 



10 
6 

-9 
-25 
-33 
-37 





-5 

-21 

-39 
-48 
-53 



-10 



-10 
-15 
-33 
-53 
-63 
-69 



-20 



-20 
-26 
-46 
-67 
-79 
-85 



Frostbite 

One common disability caused by exposure to cold is 
frostbite; i.e., localized freezing of body tissue. Frostbite can 
be either superficial, involving only the skin, or deep, 
extending below the skin. At a windchill temperature of 
-25 ° F, exposed flesh may freeze within a minute. A tem- 
perature of 5 ° F and a 15-mph wind combine to create such 
a condition. 

Performance Effects of Cold 

Cold, even if not severe enough to cause body cooling, 
can still affect performance, especially that involving motor 
skills and cognitive ability. For example, whenever hand 



114 



skin temperature falls below about 68° F, manual dexter- 
ity deteriorates rapidly. Tasks that require use of handtools 
or small parts are most affected by the cold. Localized warm- 
ing of the hands, however, can reduce the negative effects 
of cold on performance. However, if the entire body is not 
kept warm, general body shivering will interfere with the 
performance of fine motor-hand coordination tasks. 

The results dealing with the effects of cold in cognitive 
performance are less clear cut than those on motor per- 
formance. Cold is likely to decrease the performance of 
complex mental tasks that contain an element of time 
estimation (time seems to go more slowly in the cold), due 
to the distraction caused by the cold stress. 

Protection From Cold Stress 

It appears that little acclimatization to cold takes place, 
except in the case of extremely long-term exposures. The 
best protection is clothing that remains dry and insulates 
the worker against the cold. Localized warming of the hands 
using heat lamps may be beneficial under certain condi- 
tions. Adequate diet, high in carbohydrates, fats, and pro- 
tein, is also important to fend off the effects of cold. 



DISCUSSION 

This chapter has briefly reviewed the effects of illumina- 
tion, noise, whole-body vibration, and climate on miner 
health and performance. It is important to remember that 
in the mining industry, combinations of environmental 
stressors exist. Mining machines generate noise and vibra- 
tion and are often used in low-light environments. In many 
cases, these environmental factors can produce levels of 
stress that seriously degrade performance and compromise 
employee health. Technologies are available for controlling 
such environmental factors and their application is well 
within the state-of-the-art. What is needed on the part of 
the mining industry is a more active awareness of the 
severity of the problem and a commitment to reduce it. 



REFERENCES 

1. American Conference of Governmental Industrial Hygienists 
(Cincinnati, OH). Threshold Limit Values for Chemical Substances 
and Physical Agents in the Workroom Environment With Intended 
Changes for 1987-88. 1987, 114 pp. 

2. American Industrial Hygiene Association (Akron, OH). 
Heating and Cooling for Man in Industry. 2d ed., 1975, 147 pp. 

3. Antecaglia, J., and A. Cohen. Extra Auditory Effects of Noise 
as a Health Hazard. Sec. in Noise and Hearing Conservation. Am. 
Ind. Hygiene Assoc, Akron, OH, 1981, pp. 11-15. 

4. Atherley, G., and W. Noble. Effects of Ear Defenders (Ear 
Muffs) on the Localization of Sound. Brit. J. Ind. Medicine, v. 27, 
1970, pp. 260-265. 

5. Bartholomae, R.C., and R.P. Parker. Mining Machinery Noise 
Control Guidelines, 1983. BuMines Handbook, 1983, 87 pp. 

6. Belding, H, and T. Hatch. Index for Evaluating Heat Stress 
in Terms of Resulting Physiological Stress. Heating, Piping, and 
Air Conditioning, v. 27, 1955, pp. 129-136. 

7. Bell, C, M. Crowder, and J. Walters. Duration of Safe Ex- 
posure for Men at Work in High Temperature Environments. 
Ergonomics, v. 14, 1971, pp. 733-757. 

8. Bobick, T., and D. Giardino. Noise Environment of the 
Underground Coal Mine. MSHA IR 1034, 1976, 26 pp. 

9. Botsford, J. A Wet Globe Temperature for Environmental Heat 
Measurement Am. Ind. Hygiene Assoc. J., v. 32, 1971, pp. 1-10. 



10. Cain, R., and R. Pettry. Investigation of Medical Costs Cor- 
responding to Various Injuries in the Coal Industry and Subsequent 
Implications of the Need for Ergonomic Research (Paper in Pro- 
ceedings of the 1984 International Conference on Occupational 
Ergonomics, May 7-9, 1984). Human Factors Assoc, of Canada, 
Toronto, Canada, 1984, pp. 462-465. 

11. Crooks, W.W., K.L. Drake, T.J. Perry, N.D. Schwalm, B.F. 
Shaw, and B.R. Stone. Analysis of Work Areas and Tasks To 
Establish Illumination Needs in Underground Metal and Nonmetal 
Mines. Volume I of II (contract J0387230, Perceptronics Inc.). 
BuMines OFR 11HD-81, 1980, 254 pp.; NTIS PB 81-236804. 

12. Crooks, W. and J. Peay. Definition of Illumination Re- 
quirements for Underground Metal and Nonmetal Mines. Paper 
in Mine Illumination. Proceedings: Second International Mine 
Lighting Conference of the International Commission on Illumina- 
tion (CIE); comp. by K.L. Whitehead and W.H. Lewis. BuMines IC 
8886, 1982, pp. 319-333. 

13. Daniel, J.H., J.A. Burks, R.C. Bartholomae, R. Madden, and 
E.E. Ungar. The Noise Exposure of Operators of Mobile Machines 
in U.S. Surface Coal Mines, 1979. BuMines IC 8841, 1981. 24 pp. 

14. Dukes-Dubos, F., and A. Henschel. Development of Permissi- 
ble Heat Exposure Limits for Occupational Work. ASHRAE J., v. 
15, 1973, pp. 57-62. 

15. Eastman, A. A New Contrast Threshold Visibility Meter. Il- 
luminating Eng., v. 63, 1968, p. 37. 

16. Gagge, A., J. Stolwijk, and Y. Nishi. An Effective Tempera- 
ture Scale Based on a Simple Model of Human Physiological 
Regulatory Response. Am. Soc. of Heating, Refrigeration, and Air 
Conditioning Eng., New York, 1970, 22 pp. 

17. Galaitsis, A., and T. Bobick. Noise Control of an Underground 
Mine Personnel Carrier. Noise Control Eng. J., v. 21, No. 1, 1983. 
pp. 4-9. 

18. Giardino, D., and L. Marraccini. Noise in the Mining 
Industry-An Overview. MSHA IR 1129, 1981, 10 pp. 

19. Goldstein, R. An Interactive Computer System for Evaluating 
Coal Mine Illumination (contract S0271041, Mathematical Applica- 
tions Group Inc.). BuMines OFR 110-80, 1980. 21 pp.; NTIS PB 
81-125528. 

20. Modifications Made to an Interactive Computer 

System for Evaluating Coal Mine Illumination (contract H0282038. 
Mathematical Applications Group Inc.). BuMines OFR 101-81, 
1980, 27 pp.; NTIS PB 81-236754. 

21. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
Approach. Taylor and Francis, 1981, 379 pp. 

22. Henschel, A. Comparison of Heat Action Levels. Paper in 
Proceedings of NIOSH Workshop on Recommended Heat Stress 
Standards, ed. by F. Dukes-Dubos and A. Henschel. NIOSH. Cin- 
cinnati, OH, DHHS. 81-108, 1980. pp. 21-31. 

23. Kaufman, J.E. (ed.). IES Lighting Handbook: Reference 
Volume. Illuminating Eng. Soc. of North America, 1981, 481 pp. 

24. International Organization for Standardization (Paris, 
France). Guide for the Evaluation of Human Exposure to Whole- 
Body Vibration. ISO 2631, 1974, 15 pp. 

25. Hot Environments-Determination of the Web Bulb 

Globe Temperature (WBGT) Heat Stress Index. ISO-DIS 7243. 1981, 
18 pp. 

26. Jensen. P., C. Jokel, and L. Miller. Industrial Noise Control 
Manual (Rev.). NIOSH. Cincinnati. OH. DHHS 79-117. 1978. 173 

PP- 

27. Jensen, R., and D. Heins. Relationships Between Several 
Prominent Heat Stress Indices. NIOSH. Cincinnati. OH. DHHS 
77-109, 1976, 372 pp. 

28. Merritt, J.O., T.J. Perry, W.H. Crooks, and J.E. Uhlaner. 
Recommendations for Minimal Luminance Requirements for Metal 
and Nonmetal Mines (contract J0318022. Perceptronics Inc. I 
BuMines OFR 65-85, 1983, 236 pp.: NTIS PB $5-215689. 

29. Misaqi, F. Heat Stress in Mining. MSHA SM 6. 1977. 34 pp. 

30. Morris, L., R. Graves, and A. Nicholl. An Ergonomic Ap- 
proach to the Assessment of Thermal Conditions in the Mining In- 
dustry. Paper in Proceedings of the Ergonomics Society Conference 
1983, Coudau, UK, Sept. 15-18. 1983; ed. by K. Coombes. Taylor 
and Francis. 1983. pp. 77-81. 



115 



31. National Institute for Occupational Safety and Health (Cin- 
cinnati, OH). Survey of Hearing Loss in the Mining Industry. DHHS 
76-172, 1976, 145 pp. 

32. Nguyen, P. Mine Company Finds Ear Muffs Overrated by 
Manufacturer. Natl. Saf. Coun. Min. Newsletter, Nov. -Dec. 1984, 
p. 6. 

33. Oborne, D. Ergonomics at Work. Wiley, 1982, 321 pp. 

34. Ramsey, J., C. Burford, M. Beshir, and R. Jensen. Influence 
of Thermal Environment on Safety Behavior. Ergonomics, v. 25, 
No. 6, 1982, p. 528. 

35. Ramsey, J., and C. Chai. Inherent Variability in Heatstress 
Decision Rules. Ergonomics, v. 26, 1983, pp. 495-504. 

36. Remington, P.J., D.A. Andersen, and M.N. Alakel. Assess- 
ment of Whole Body Vibration Levels of Coal Miners. Volume II: 
Whole Body Vibration Exposure of Underground Coal Mining 
Machine Operators (contract J0308045, Bolt Beranek and Newman 
Inc.). BuMines OFR 1B-87, 1984, 114 pp.; NTIS PB 87-144119. 

37. Sataloff, J., and P. Michael. Hearing Conservation. Charles 
C. Thomas, 1973, 376 pp. 

38. Schutte, P., J. Hitge, A. Kielblock, and N. Strydom. Produc- 
tive Acclimatization: II. A Code of Practice for Heat Tolerance 
Testing and Micro-climate Acclimatization (Rev.). Chamber of 
Mines, Johannesburg, South Africa, Rep. 5/82, 1982, 17 pp. 

39. Simons, A., A. Radke, and W. Oswald. A Study of Truck Ride 
Characteristics -in Military Vehicles. Bostrom Res. Lab., 
Milwaukee, WI, 1956, 123 pp. 

40. Siple, P., and C. Passel. Movement of Dry Atmospheric Cool- 
ing in Subfreezing Temperature. Proc. Am. Philosophical Soc, v. 
89, 1945, pp. 177-199. 



41. Strydom, N. Developments in Heat-Tolerance Testing and 
Acclimatization Procedures Since 1961. Paper in Proceedings of 
the 12th CMMI Congress, ed. by H. Glen. Geol. Soc. South Africa, 
Johannesburg, South Africa, Chamber of Mines, 1982, pp. 235-241. 

42. Strydom, N., D. Mitchell, A. Van Rensburg, and C. Van 
Graan. The Design, Construction, and Use of a Practical Ice- Jacket 
for Miners. J. South African Inst. Min. and Metall, v. 75, 1974, pp. 
34-37. 

43. Strydom, N., P. Schutte, and A. Kielblock. Productive Ac- 
climatization: I. A Code of Practice for the Selection of Workers 
Based on Physical Work Capacity (Rev.). Chamber of Mines, Johan- 
nesburg, South Africa, Rep. 49/81, 1981, 7 pp. 

44. Trotter, D. The Lighting of Underground Mines. Gulf, 1982, 
216 pp. 

45. U.S. Mine Safety and Health Administration. Handbook of 
Underground Coal Mine Illumination Requirements. 1980, 30 pp. 

46. Van der Walt, W. A Survey of the Incidence of Heat Stroke 
in the Gold Mining Industry over the Period 1969 to 1980. Chamber 
of Mines, Johannesburg, South Africa, Rep. No. 15/81, 1981, 41 pp. 

47. Van Graan, C. Some Applications of Ergonomics in the South 
African Mining Industry. South African Mech. Eng., v. 24, 1974, 
pp. 282-289. 

48. Wasserman, D. Occupational Vibration Studies in the U.S.— 
A Review. Sound and Vibration, v. 14, 1980, pp. 21-24. 

49. Whitehead, K.L., and W.H. Lewis. Paper in Mine Illumina- 
tion. Proceedings: Second International Mine Lighting Conference 
of the Commission on Illumination (CIE); comp. by K.L. Whitehead 
and W.H. Lewis. BuMines IC 8886, 1982, pp. 1-10. 



116 



CHAPTER 9.— TRAINING 




Training is an important and expensive enterprise in the mining industry. 



Human factors seeks to modify the job to fit the person, 
while training seeks to modify the person to fit the job— in 
this sense the two oppose one another. Conversely, a well- 
designed (human-factored) job reduces the requirements for 
training, and an effective training program can reduce the 
human factors design requirements— in this sense they 
complement one another. It would be impractical, if not im- 
possible, to design a job in such a manner that no training 
was required. By the same token, it would be extremely un- 
wise to expect the training function to overcome all human 
factors deficiencies present in the design of a job. The fact 
is that both human factors and training are necessary for 
efficient and safe operations. 

Both human factors and training seek to change be- 
havior; human factors does it through design, while train- 
ing does it by modifying skills, knowledge, and attitudes. 
In addition to the commonality of goals, human factors also 
has a role in the design of effective training programs. A 
training program can be viewed as any other system, and 
human factors can contribute to the design of such a system. 
Human factors has contributed to (1) the design of train- 
ing hardware, such as simulators and training aids, (2) 
determining training needs, and (3) evaluating the effec- 
tiveness of the training programs. 

Training is an important and expensive enterprise in 
the mining industry. In 1983, for example, the U.S. mineral 
industry employed over 400,000 miners and provided ap- 
proximately 4.5 million hours of formalized health and 
safety instruction. In addition, the U.S. mining industry pro- 
vided over 80,000 miners with occupational training to 
support organizational goals and comply with Federal and 
State training requirements. The mining industry spends 



approximately $200 million on new hire, refresher, and 
occupational training per year (2D. 1 



EFFECTIVENESS OF TRAINING 

Assessing the effect of training on behavior is a difficult 
task in the operational environment. Several problems pre- 
sent themselves that make the interpretation of results dif- 
ficult. First is the problem of defining what is meant by 
training. Often, a training program involves several com- 
ponents, including classroom training, on-the-job training, 
and company support programs such as safety campaigns. 
It is difficult to determine which components of a program 
are effective and which are not. 

A second problem is one of experimental control. Often, 
a control group (i.e., untrained miners) is not used, mak- 
ing it impossible to determine what the injury or produc- 
tion rates would have been without the training. Usually, 
only before- and after-training measurements are made. 
Factors in the work setting, other than training, may have 
changed at the same time that training was started and 
could have influenced safety or productivity. 

A third problem is that the measures used to evaluate 
the effect of training may not be sensitive enough to detect 
real changes in behavior. Both injury rate and production 
rate are influenced by all sorts of factors, including luck, 
or lack of it. A crew may be working more safely and more 
efficiently, but because of extenuating circumstances (e.g., 



1 Italic numbers in parentheses refer to items in the list of reference* at 
the end of this chapter. 



117 



poor roof conditions, equipment breakdown, outbreak of flu), 
its safety and productivity records do not reflect the positive 
effects of training. 

With these problems in mind, a review is made of a few 
studies that have attempted to assess the effects of train- 
ing on behavior. One conclusion from the literature is that 
generalized training is not as effective as training targeted 
to change specific behaviors. A second conclusion is that 
a coordinated, multifaceted program, involving classroom 
training, on-the-job training, and followup, is more effec- 
tive than a single-shot training experience. 

The results of a maintenance training program in South 
African mines were reported by Robertson (22). In a 3-week 
course, rock cutter operators were trained to diagnose faults 
in their machines using a step-by-step troubleshooting pro- 
cedure, and to repair the malfunctions without aid from 
maintenance workers. Maintenance worker involvement in 
repairs decreased from 46% to 3%. Average repair times 
were reduced by 21%, and productivity increased by 30%. 

The outcome of a forklift training program targeted at 
specific unsafe behaviors was discussed by Cohen (5). The 
program involved a classroom presentation of incorrect and 
correct ways to handle specific hazardous situations, group 
discussion of the recommended behaviors, and a final test 
in which all members of the group scored each other as they 
performed a series of tasks using a forklift. In addition, on- 
the-job daily feedback in the form of verbal and posted 
summaries of group performance (percentage of correct 
behaviors on the job) was given to the group. The super- 
visor, in a positive, constructive, and confidential manner, 
coached the workers on correct work procedures. Results 
showed reductions in unsafe behaviors of 70% and 40% at 
two separate companies where the program was applied. 

A structured 2- to 3-day training program with on-the- 
job training, using a continuous miner simulator, was 
reported by Morris (19). After training, production increased 
an average of 7.15 st per month, per unit-shift. 

The results of a study conducted at four salt mines in 
which supervisors were trained to use social reinforcement 
(praise) to increase safe behaviors were presented by Uslan 
(27). The training program was general in nature, rather 
than targeted to specific behaviors. Eye, hand, and back in- 
juries were monitored before and after training of the super- 
visors. The results were mixed. Injuries declined at two 
mines, remained relatively stable at one, and increased in 
the other mine. The lack of clearcut results was probably 
due, in part, to the nonspecific nature of the training, and 
to the fact that the training was directed toward changing 
the behavior of supervision rather than that of the workers. 



TRAINING: WHAT IS REQUIRED 

In the United States, miner training regulations are 
described in the Federal Mine Safety and Health Act of 
1977, as amended. In addition, some States have also es- 
tablished regulations for miner training. A brief review of 
the essential features of these requirements will be pre- 
sented as well as a comparison with those set forth in other 
countries. This section should not be considered a complete 
review of existing regulations, nor should it serve as a 
substitute for the actual regulation of governing bodies. 



Training Requirements in the United States 

The Federal training regulations for new underground 
miners set forth a minimum of 40 h of training, of which 
32 h are classroom training and 8 h are at the jobsite. Eight 
hours of training must be received before a new miner can 
go underground. For new surface miners, Federal regula- 
tions specify only a minimum of 32 h of training, of which 
8 h occur before miners begin their actual work assign- 
ments. In addition, 8 h of annual refresher training is re- 
quired of all miners. The topics required for training new 
miners, newly employed experienced miners, and annual 
refresher training are listed in table 9-1 for both under- 
ground and surface mining (9). 

Besides the Federal training regulations, some States 
impose additional requirements. Of the 15 States that pro- 
duce coal in the United States, only five have requirements 
beyond the Federal regulations. Kentucky requires 90 work- 
ing days of experience, within sight and sound of a certified 
miner, followed by an examination for certification. Indiana 
requires a 6-month apprenticeship with an experienced 
miner before a new miner can work alone. Pennsylvania 
requires 1 yr of apprenticeship under close supervision, 
followed by an oral, practical examination. Illinois requires 
a 1- to 2-yr (maximum) apprenticeship, followed by oral and 
written examinations, and first-aid and mine rescue train- 
ing; those with an associate degree in coal mine technology 
or a bachelor's degree in engineering can waive 6 months 
of apprenticeship. West Virginia requires 80 h of instruc- 
tion, followed by an examination to qualify as an apprentice; 
the new employee then works 6 to 8 months (maximum), 
within calling distance of a foreman, assistant foreman, or 
designated experienced miner (20). 

Training Requirements in Other Countries 



An excellent review of training requirements and prac- 
tices in foreign countries was provided by McAteer (16). No 
attempt will be made to provide all the details of the various 
foreign training requirements here, only brief overviews 
for a few of the major European countries will be given. 

Great Britain has some of the most comprehensive train- 
ing requirements of any country. New miners must receive 
100 days of training before they can work underground, and 
they cannot work within 30 ft of the face until they have 
completed 120 days of training. To become a certified miner 
requires 3 yr, including over 300 days of formal instruction 
and 100 days of work under constant supervision. 

The Federal Republic of Germany requires a 3-yr ap- 
prenticeship, including formal schooling 3 days per week. 
Six months of training is required before a miner is per- 
mitted to work underground. In addition, 20 days of above- 
ground training, under simulated mining conditions, is also 
required. When workers are away from their jobs for 6 
months, 20 days of training is required (10 classroom and 
10 at the face) before they can resume work. 

In Poland, prospective miners enter mining school at 
the age of 14 or 15 and take 3 yr of classroom and job in- 
struction. A 3-yr apprenticeship is required, including 200 
h of training at a mine training center. Sixteen hours of 
annual refresher training is required of all miners. 



118 



Table 9-1 .—Content of underground and surface mine health and safety training, by type (9) 



Topic 



Introductory for — 



New 
miners 



Newly em- 
ployed expe- 
rienced miners 



Annual 

refresher 

for working 

miners 



UNDERGROUND 



Statutory rights and responsibilities of supervisors 

Self-rescuer and respiratory devices 

Entering and leaving the mine, transportation, communication 

Introduction to the work environment 

Mine map, escapeways, emergency evacuation, barricading . . 

Roof and ground control, ventilation plans 

Health 



Cleanup, rock dusting 
Hazard recognition . . . 
Electrical hazards .... 
First aid 



Mine gases 

Health and safety aspects of assigned tasks . 

Mandatory health and safety standards 

Prevention of accidents 

Explosives 



SURFACE 



Statutory rights and responsibilities of supervisors 

Self-rescue and respiratory devices 

Transportation and communication 

Introduction to the work environment 

Escape and emergency evacuation, firewarning and firefighting 

Ground control, highwalls, water hazards, pits and spoil banks, illumination and night work 

Health 

Hazard recognition 

Electrical hazards 

First aid 

Explosives 

Health and safety aspects of assigned tasks 

Mandatory health and safety standards 

Prevention of accidents 




France has no specific training requirements. However, 
training usually includes 2 weeks of surface classroom train- 
ing and an examination, 3 to 4 months of training at an 
underground training face, and 2 to 3 months of working 
under close supervision at an actual production face. 

Discussion 

From even this short overview of training requirements, 
it is obvious that the U.S. requirements fall short of those 
in other countries. Some authorities suggest that this ac- 
counts, in great part, for the lower injury and fatality rates 
per million labor-hours experienced by European countries. 
The fact that so many countries do require extensive new- 
miner training and apprenticeship suggests that more could 
be done in the United States to instill good working habits 
in new miners. 



TRAINING PRACTICES IN THE UNITED STATES 

In the previous section, training requirements in the 
United States and other countries were discussed. In this 
section, a brief overview of U.S. training practices is pre- 
sented. In essence, this is how the mining industry is 
meeting and, in many cases, exceeding the training require- 
ments placed on it by the Government. Over the years, a 
few studies have attempted to summarize the mining in- 
dustry's training experiences. Training at over 300 mines 



was reviewed by Adkins (7), while Digman (9) reviewed 
classroom training practices at 14 sites. Major sources of 
mine-related training in the United States were reviewed 
by Short (24). Several general themes emerge from these 
reports. 

1. The first-line supervisor plays a central role in most 
training programs conducted by the mines. 

2. There is a danger that technical compliance with 
Government training regulations assumes more importance 
than the goal of reducing mine accidents. 

3. There is tremendous diversity among programs in 
terms of resources allocated, methods used, competency of 
instructors, and use of followup methods. 

4. Instructional skills among trainers seem to be less well 
developed than are technical skills. 

5. On-the-job training is used extensively , but is often dif- 
ficult to monitor, correct, or improve when it is inadequate. 

6. Training is provided by mine companies, vocational 
schools, State agencies. Mine Safety and Health Adminis- 
tration (MSHA), equipment manufacturers, consultants, 
and trade associations, with mining companies providing, 
far and away, the majority of the training. 

7. It is difficult to demonstrate, statistically, that one 
training method is better than another for reducing 
accidents. 

Keeping in mind the diversity of training that exists 
in the mining industry. Adkins (1\ nevertheless, repre- 
sented a typical new underground miner indoctrination 
training experience. The description is worthwhile and is 



119 



reproduced here to give a conception of the methods used 

most often in miner training. 

The process begins with the personal safety equip- 
ment—hard hat, protective glasses, safety boots, leg 
bands, belt and self rescuer. The new man is shown, 
lectured on, and issued this equipment. Use of the self 
rescuer is shown in film, on poster and demonstrated 
by each individual, and then, as shown by too many 
disasters, forgotten. Next comes a brief introduction 
to the mine environment (including the geology, mine 
plan, ventilation, roof control and mining methods) 
through lectures aided by various slides, films or 
tapes, posters, mock-ups, and charts. This will be 
followed by a mine tour to illustrate and reinforce 
what the new man has been told by the instructor in 
the classroom. 

Most new employee programs continue the indoc- 
trination with lectures and demonstrations covering 
the topics of oxygen deficiency and methane detection 
devices and first aid. Films, posters, and simulation 
devices are used to supplement the lecture presenta- 
tions and to give the student an opportunity for 
"hands on" experience, as feasible. More lectures from 
various company departments on organizations and 
policy, and from state and union representatives on 
the local laws and working agreement, plus some 
qualification testing, will constitute the balance of 
new employee indoctrination. Other than exposure to 
slogans and either monthly (the usual case) or weekly 
safety meetings, the average miner will not receive 
any more classroom training unless he needs annual 
qualification or moves on to maintenance or supervi- 
sion duties. 



CHARACTERISTICS OF SUCCESSFUL 
SAFETY PROGRAMS 

There have been several attempts to identify character- 
istics of successful safety programs. The approach taken has 
been to either examine exemplary safety programs or to 
compare companies having high and low accident rates. For 
example, 192 Wisconsin factories with high and low acci- 
dent rates were compared by Cohen {4); two successful task 
training programs in two open-pit taconite mines were 
described by Couillard (6); and safety directors of 12 coal 
companies that had won awards for extended periods of 
work without lost-time injury were interviewed (8). In ad- 
dition to these studies, a review of the literature available 
up to 1977 was provided by Cohen (3). 

These various studies and reviews show remarkable con- 
sistency with respect to the characteristics of successful 
safety programs. One conclusion that stands out is that 
there is more to a successful safety program than just train- 
ing. For purposes of this presentation, the characteristics 
of successful safety programs will be divided into three 
classes: management, training and incentives, and accident 
reduction. 

Management 

The most consistent finding in all the studies investi- 
gating successful programs is management commitment. 
Top management must be sincerely committed to reducing 



injuries, and be willing to back up that commitment with 
resources and support. Other management-related charac- 
teristics of successful programs reported in the literature 
follow. 

1. Safety personnel were part of top management, and 
adequate staff was available to carry out the safety func- 
tion. The ranking safety official was not subordinate to pro- 
duction personnel. 

2. Active safety committees were supported by manage- 
ment, and there were provisions for short, daily safety 
meetings. 

3. Close, frequent contacts between workers and super- 
visors or foremen were evident, enabling open communica- 
tion on safety and other job-related matters. 

4. A more humanistic attitude toward disciplining vio- 
lators of safety rules was evident. In disciplinary actions, 
measures other than suspension were used more often. 

5. There existed a well-developed selection and job place- 
ment system that matched worker capabilities to job 
demands. 

Training and Incentives 

Several factors emerged from the literature relative to 
the conduct of training and safety incentive programs. 

1. Formal training must be reinforced, on the job, by first- 
line supervisors. 

2. A mixture of different safety activities (e.g., training, 
safety promotional campaigns, off-the-job safety activities, 
inspections) is more effective than concentrating on only 
a few. 

3. Trainers must be trained to train. 

4. The primary goal of training should be improved job 
performance, of which safety is one part. 

5. There must be a readiness to change and modify train- 
ing programs to keep up with changing needs. 

6. Training programs should be competency-based so that 
workers are evaluated on their ability to perform their jobs. 

7. Greater opportunities should be made available for 
general and specialized job and safety training. 

8. Greater efforts must be made to influence the safety 
consciousness of workers by enlisting family and community 
involvement in company safety campaigns. 



Accident Reduction 

Successful programs usually include activities designed 
to reduce accidents, such as the following. 

1. High levels of housekeeping and orderly workplace 
conditions. 

2. Application of engineering controls, as well as non- 
engineering techniques, to reduce accidents. (Engineering 
controls include good human factors design of equipment, 
environments, and procedures.) 

3. More frequent formal inspections of worksites. 

4. Continual examination and modification of safety rules 
to improve their effectiveness. 

5. Well-developed procedures for reporting and investi- 
gating accidents. 

Undoubtedly, all of these factors contribute to a success- 
ful program. Unfortunately, it is not possible to say which 
factors are the most critical or which are simply the conse- 
quence of others. Management commitment, however, is 



120 



probably the most important factor, because all the others 
are dependent on management approval. 



BASIC CONCEPTS IN HUMAN LEARNING 

There exists a vast amount of research literature, span- 
ning more than 100 yr, that deals with human learning. 
For the most part, the research involves laboratory studies 
of relatively simple learning tasks. The applicability of 
much of the literature to complex, real-world learning situa- 
tions is tenuous. Over the years, there have been numerous 
attempts at developing theories to explain human learn- 
ing; but, unfortunately, none of them has accounted for all 
the intricacies involved in the process. What has emerged 
from the research literature and theory building is a set 
of concepts and basic principles that appear to be valid in 
a wide range of learning situations. The purpose of this sec- 
tion is to introduce the more important concepts and prin- 
ciples to provide a basis for understanding the learning 
process and the role of training. 

Learning Versus Performance 

The learning process is never directly observed. Instead, 
it is found that learning has taken place by observing an 
individual's behavior prior and subsequent to experiences 
called training. What this means is that it is not known 
whether individuals have learned until they have per- 
formed. The verbal statement, "I understand how to do 
that," should not substitute for actual performance. A per- 
son demonstrates the acquisition of a skill by performing 
a skilled act. Any training method that does not provide 
ample opportunity for the trainee to perform allows little 
opportunity for the trainer, or trainee for that matter, to 
determine what has been learned and what has not been 
learned. 

Performance Feedback 

People usually do not make an effort to change or im- 
prove their behavior unless they perceive that it needs to 
be changed or improved. Job performance often deteriorates 
so slowly that no one really notices. However, once workers 
are made aware that their performance has deteriorated, 
they usually improve quickly, assuming, of course, that they 
have the skills and support necessary to improve. 

To provide performance feedback requires that a per- 
son's behavior be observed, quantified, and presented in a 
meaningful way. For example, the mean time to complete 
a task or number of reworks might be the type of perfor- 
mance data to feed back to maintenance workers. The in- 
cidence of unsafe behavior is an appropriate measure for 
all workers. Whatever the performance measure used, it 
must be observable so that it can be measured; quantifiable, 
to permit the use of summary statistics; reliable, to the ex- 
tent that everyone observing the behavior agrees whether 
or not it occurred, or to what degree it occurred; and valid, 
so far as it relates to the goal to be maximized, e.g., safety, 
productivity, maintenance efficiency. 

For example, a study in a bakery to assess the effec- 
tiveness of training and performance feedback on the in- 
cidence of safe behaviors was performed by Komaki (13). 
The approach illustrates how performance feedback can be 
used to modify behavior. First, accident reports were re- 
viewed, hazards clearly defined, and workers closely ob- 



served to determine which specific areas needed the most 
attention. From this preliminary analysis, specific unsafe 
behaviors were targeted for modification. This is an impor- 
tant point; the training and feedback were not comprehen- 
sive or general in nature, but rather dealt with a set of 
explicit behaviors and situations. 

To assess the effect of this program, baseline data were 
collected for 5.5 weeks. During this period, the incidence 
of safe behaviors was recorded. The intervention or treat- 
ment involved a training component that consisted of a slide 
presentation dealing with the hazards and tasks and showed 
how to perform the tasks safely. A list of the safe behaviors 
was given to each worker. This is also an important point; 
training focused on what should be done, rather than just 
what should not be done. Too often a safety training pro- 
gram overstresses the negative, "don't do this, don't do 
that," but never really tells the trainee what to do or how 
to do it correctly. 

In addition to the training, performance feedback was 
given of the percentage of times safe behaviors were used 
on the job. Workers were shown a graph of the results of 
the baseline observations that indicated that they had been 
performing safely about two-thirds of the time. The graph 
was posted with an unplotted section to be completed as the 
intervention phase progressed. The intervention phase 
lasted for 11 weeks, at which time a reversal phase was 
introduced. 

During the reversal phase, feedback was discontinued, 
but the list of safety reminders remained. Figure 9-1 shows 
the results of the experiment. As can be seen, the incidence 
of safe behavior improved dramatically during the interven- 
tion period, and remained high until the performance feed- 
back was discontinued during the reversal phase. In a subse- 
quent study (14), the effect of safety training, apart from 
performance feedback, was assessed. The study found that 
while safety training alone resulted in improved perfor- 
mance, training combined with feedback yielded even bet- 
ter performance. Cohen (5), in a carefully developed study, 
reported similar results for safe forklift operation. This 
study, however, found that the incidence of safe behavior 
remained high for months after feedback was discontinued. 
This was attributed to the development of informal peer 




RMrari 



OBSERVATION PERIODS 

Figure 9-1.— Results of an experiment that demonstrates ef- 
fectiveness of performance feedback on incidence of safe 

behaviors (13). (Copyright 1978 by the American Psychological Association and 
reprinted by permission of the author) 



121 



group norms that stressed and accepted the safe methods 
of performing the job. In essence, the safe way became the 
accepted, normal way of doing the work (the dream of every 
safety director). 

One of the most common findings about performance 
feedback is that it affects motivation. Studies have shown 
that compared to trainees given no feedback, those receiv- 
ing some feedback were less bored, reported for training 
more frequently on time, and had more favorable attitudes 
toward the training. 

The amount and the timing of feedback in the training 
process is critical. Burdening a trainee with too much in- 
formation may be as bad as not providing any information. 
The new trainee may be able to absorb only a small amount 
of information. Too much detail can be both confusing and, 
because of initial inadequate performance, discouraging. 

Reward and Punishment 

A general axiom of human behavior is that people tend 
to repeat behaviors that are rewarded (positive reinforce- 
ment). The practical problem is that what is rewarding to 
an individual is not always known. A person may engage 
in a particular behavior for any of a number of reasons, such 
as to receive positive recognition from a supervisor, to 
reduce the time required to complete a task, to appear dar- 
ing because he or she likes to take chances, or to receive 
positive recognition from a work group engaging in the 
behavior. To be effective, positive reinforcement should be 

(1) given as soon as possible after a behavior has occurred, 

(2) valued by the person, and (3) specific and directed to a 
particular behavior. For example, being told by a supervisor 
who is not respected that one has done a good job probably 
would not be very reinforcing. Telling workers at the end 
of shift that they did a good day's work would do little to 
reinforce specific behaviors of individual workers. Providing 
a year-end bonus is too far removed in time from the occur- 
rence of the behaviors one is trying to reinforce to be very 
effective. A bonus based on overall mine productivity or 
safety probably is an ineffective reinforcer, because an in- 
dividual worker cannot relate the reward to his or her 
behavior. 

One thing is certain, if a behavior has been reinforced 
and reinforcement is discontinued, the behavior will disap- 
pear. That is, the frequency of the behavior will decrease, 
and eventually the behavior will subside. This is called ex- 
tinction. It is important, therefore, that the work situation 
be structured so that behaviors acquired during training 
will be reinforced on the job by supervisors, coworkers, etc. 

With respect to extinction of behaviors following cessa- 
tion of reinforcement, it is well accepted that a behavior 
will persist longer if the original reinforcement was inter- 
mittent rather than continuous. In the real world, it is im- 
possible for a supervisor to give positive reinforcement each 
time a job is done well; and, in fact, it is probably better 
that it not be done every time. Eventually, the supervisor 
will not be able to reinforce the behavior; but, the behavior 
will persist longer if the supervisor did not always reinforce 
the worker in the past. 

An example of the use of positive reinforcement to 
change behavior comes from a study performed in four salt 
processing plants by Uslan (27). First-time supervisors were 
trained in the systematic application of positive reinforce- 
ment in the form of verbal praise to increase the frequency 
of safe work behaviors. The results indicated a reduction 



in injuries at two sites and no reduction at the other two 
sites. When the data were corrected for hours worked, a 
third site showed a reduction in injuries. The results were 
not overly dramatic; but, upon reflection, this is not sur- 
prising. The problem was that the behaviors were the target 
of the praise, but the number of accidents was the measure 
used to assess the effects of the praise. The relationship be- 
tween behaviors and accidents is not perfect. The reinforce- 
ment may have been very effective in increasing the inci- 
dence of safe behavior; but, due to other circumstances (e.g., 
work practices, environmental conditions), accident rates 
may not have decreased significantly. It is for this reason 
that safety program effectiveness is better judged by assess- 
ing the effect on behavior, rather than by tallying accidents. 
An effective safety program would be expected to reduce 
accidents, but assessing the effect on behavior provides a 
more immediate and valid measure of effectiveness. Simi- 
larly, a job skills training problem is better evaluated based 
on behavior changes than on productivity. 

The use of punishment is not the same as failing to rein- 
force. The evidence suggests that punishment inhibits 
behavior rather than eliminating it, as would be the case 
for behaviors that are not reinforced. In the case of punish- 
ment, a behavior that leads to the avoidance of the punish- 
ment is reinforced. Often, failure to reinforce a negative 
behavior may have a better long-range effect than would 
a reprimand (punishment) from a trainer, even though the 
reprimand gives the trainer some temporary relief or sat- 
isfaction. There are at least three reasons for this. 

1. Punishment may suppress a behavior, but the be- 
havior may appear again if the source of punishment is not 
present at a later time. 

2. Punishment can be disruptive and have its effects on 
larger behavioral segments than on an undesired behavior 
itself. 

3. Repeated punishment from the same person may have 
the effect of altering the perception of that person, so that 
he or she is avoided and loses his or her effectiveness as 
a source of positive reinforcement. 

Perhaps the most efficient use of punishment would be 
to combine mild and informative punishment for an incor- 
rect behavior with reward for a correct behavior. 

Learning From Models and Examples 

People learn vicariously through observing behavior of 
others and the consequences of that behavior. The literature 
on vicarious learning and its application to on-the-job train- 
ing in the mining industry was reviewed by Thurlow (25). 
The notion of a model involves a person or persons who set 
a standard of performance that others try to attain. A model 
can be a supervisor, coworker, relative, or famous person. 
Research has found that people tend to favor models similar 
to their own ability over those whose behavior they can 
match only through great effort. People exposed only to high 
standards are more likely to adopt them than people ex- 
posed to conflicting standards. Further, the high standards 
set by a model are less likely to be adopted by trainees if 
the model imposes lenient standards on himself or herself. 

The practical implications of this are that supervisors, 
trainers, and other models should adopt a consistent stan-^ 
dard of behavior; and they must be willing to meet that stan- 
dard in their work. Telling workers to "do what I say, not 
what I do," is unlikely to make much of a positive impres- 
sion on them. 



122 



METHODS OF TRAINING 

Although there are many ways of categorizing training 
methods, this section is organized by the degree to which 
each method approximates the actual working conditions 
under which a trainee will ultimately work. There are all 
sorts of training methods, but this section will concentrate 
on only six: classroom, part-task simulation, full-task 
simulation, simulated mine environments, training sections 
in an actual mine, and on-the-job training. This list is 
ordered from the most removed from the actual work situa- 
tion to the actual work situation itself. The objective of this 
section is to present some data and examples of each of these 
training methods as they apply to the mining industry. 

Most mine training programs use several of these train- 
ing methods; the most common combination is probably 
classroom training followed by on-the-job training. 

Classroom Training 

Classroom training has always been a part of miner 
training, and appears to be gaining additional popularity 
as a prime method of presenting new-worker orientation 
and safety training mandated by Government agencies. 
Traditionally, classroom training involves a lecture- 
discussion format, supplemented by films, slide presenta- 
tions, and equipment mockups and models. Trainees may 
or may not be tested to assess their level of learning. In some 
cases, trainees may have an opportunity to practice a skill; 
for example, putting on a self-rescue device. 

The major shortcoming of classroom training is that, in 
most cases, the trainee is a passive receiver of information 
and has no opportunity to practice what has been learned 
in a realistic setting. The major advantage is that a great 
deal of information can be imparted to a large number of 
people, inexpensively. Classroom training is probably best 
suited for presenting overview and general orientation in- 
formation, or for promoting group discussion and develop- 
ing group norms and attitudes. 

A survey of 108 apprentice miners in West Virginia (18) 
showed that miners liked classroom training, thought it was 
valuable, and preferred study within a group rather than 
self-study. However, these same miners strongly preferred 
self-paced instruction, which is difficult to implement in a 
group situation. The miners recommended using short text- 
books and tests for each part of a course, but felt that study- 
ing was valuable even without examinations. They also 
liked movies and felt they learned best when movies were 
used. Unfortunately, this survey did not assess whether 
movies, indeed, resulted in better learning. 

Part-Task Simulation 

Part-task simulation extracts from an entire task or job 
a small part for training. Part-task simulators usually con- 
sist of hardware devices that give a trainee an opportunity 
to practice, over and over, one part of an overall task. An 
example of a part-task simulator is the onboard simulator 
of abnormal conditions (OBSAC) developed under a Bureau 
of Mines contract (15). This device, shown in figure 9-2, is 
used to train haulage truck drivers to recognize and respond 
to abnormal equipment conditions. The OBSAC, which is 
electrically connected to the mobile equipment via an 
adapter kit, allows the instructor to control the readings 
of certain gauges, actuate visual and audible alarms, and 
degrade braking and steering performance. Functional 



gauges of the OBSAC prototype include water temperature, 
oil pressure, voltmeter, transmission-converter oil temper- 
ature, transmission-clutch oil pressure, starting air pres- 
sure, and brake air pressure. A digital stopwatch, part of 
the console, enables the instructor to determine the reac- 
tion time of trainees to observe an emergency or abnormal 
condition and initiate the proper action. 

The OBSAC training is blended into the general haul- 
age, loading, and dumping procedures; that is, once a 
trainee starts handling rock in a normal operating man- 
ner, the instructor adjusts a gauge by a certain amount. 
A good example is the engine oil pressure; the instructor 
intentionally adjusts the gauge so that it does not rise upon 
startup. If, on startup, trainees do not observe the engine 
oil pressure within 5 s, they lose three points. During nor- 
mal operation, the instructor may drop the reading 25 psi, 
and if the trainee does not notice it within 15 s, he or she 
loses points. 

Field tests of OBSAC were carried out at two surface 
minesites (1 1 ). The overall reaction to the OBSAC was very 
favorable among the trainees because it vividly simulated 
abnormal situations in a realistic operational setting. One 
major advantage of this device is that abnormal conditions 
are presented at will, and the reactions of the trainees are 
observed under a variety of conditions. This part-task 
simulator is somewhat unique in that it is operated in the 
actual work environment. 

Full-Task Simulation 

Full-task simulations involve simulating all, or a signifi- 
cant portion, of a job in a training environment. Typically, 
such simulators are very expensive and complex. Their 
main advantages are that they allow the instructor to 
develop specific training exercises to meet the capabilities 
of the students; they allow the students to practice exer- 
cises over and over again; they provide integrative train- 
ing; and they permit learning in a safe, standardized envi- 
ronment where student errors will not destroy equipment 
or endanger lives. 

An example of a full-task simulator is the shuttle car 
training systems (SCTS) developed under a Bureau of Mines 
contract (23). Figure 9-3 shows a cutaway diagram of the 
SCTS. It is designed to provide control, familiarity, and 
practice in procedures associated with tramming, turning, 
loading, and dumping. The system includes inby and outby 
projector systems that show actual in-mine environmental 
conditions, and are tied to the shuttle car controls. This 
enables the trainee to perceive and judge the relationship 
of the shuttle car to corners and intersections, and to ma- 
neuver through work sections. The simulator also provides 
bumping and pitching movement, as well as integrated 
sounds and vibration system, all computer controlled. 

Simulated Mine Environments 

Part- and full-task simulators attempt to reproduce the 
equipment used in mining, usually in an environment far 
removed from the actual working environment. OBSAC is 
an exception in that it is used in an actual mine environ- 
ment. Full-task simulators often only reproduce the visual 
aspects of an environment. Simulated mine environments 
offer an opportunity to conduct training in a systematic, 
planned fashion, without being concerned with production 
demands, changing conditions, etc. In Europe, training 
galleries (simulated mine environments^ are more common 



123 




Figure 9-2.— OBSAC part-task simulator held in instructor's lap in port seat of a haulage vehicle (15). 



Inby remedial 
system 



Curved screen 




Outby 
remedial 
system 



Outby projection 
system 



Bumping 
and pitching Operator's 
pit 

Electronics 
cabinet 



Inby projection 
system 



Sloping Curved screen 
floor. 




Figure 9-3.— Shuttle car training system full-task simulator (29). 

than in the United States. Some European mine rescue sta- 
tions use them to train rescue teams. In some, smoke can 
be pumped into the simulated mine for additional realism. 
One example of a U.S. simulated underground mine was 
built by U.S. Steel at its Cumberland Mine (12). It consists 
of four entries and three crosscuts, and contains a power 
center, fans, continuous miner, conveyor belt, shuttle car, 
scoop car, and roof bolter. Students with no experience prac- 
tice jobs such as rock dusting, posting, building stoppings, 



and hanging brattice cloth. This simulated mine is also used 
to train experienced miners in the use of new equipment, 
and to develop teamwork in a section crew. 

Training Sections in an Actual Mine 

Several companies have allocated sections of their mines 
strictly for training purposes, which is a cost-effective alter- 
native to building a simulated mine environment. Here, 
training can be conducted without the pressures and con- 
straints inherent in using actual production sections for 
training. An additional advantage is that efficiency is usu- 
ally increased; that is, the necessary materials are avail- 
able, and several trainees can engage in a task at one time, 
while others observe. A trainee can be stopped when an er- 
ror is made and instructed in the proper manner of perfor- 
mance, without concern for productivity. The sequence of 
training tasks can be controlled and need not be compro- 
mised because of production demands. 

On-the-Job Training 

The most commonly used, and abused, method of train- 
ing in the mining industry is on-the-job training (OJT). OJT 
encompasses informal procedures, wherein a new worker 
is assigned to an experienced worker to follow around and 
learn the ropes. Such training is often unstructured, 



124 



haphazard, and incomplete. The senior person may perceive 
the new miner as a hindrance who is taking valuable time 
away from the primary goal— productivity. OJT may include 
a structured program where workers are assigned specific 
sequences of tasks, and are monitored and evaluated by peo- 
ple whose primary responsibility is training. 

An example of structured OJT is the job safety skills 
training (JSST) program at Monterey Coal Co. (17). The 
training is conducted by a specially trained team on the 
working section. JSST team members give close personal 
attention to the safety performance and attitudes of in- 
dividual miners in the unit as they go about their work 
routines. As part of the training, a mock emergency is 
staged (the foreman is injured) to force the workers to decide 
for themselves what must be done. The focus is on building 
teamwork and leadership rather than testing first-aid pro- 
cedures. Monterey Coal reports a 50% reduction in nonfatal- 
days-lost injuries since the program started. 

OJT often generates high levels of motivation in stu- 
dents; and, because the training is taking place in the ac- 
tual work environment, transfer of training to everyday 
work is almost assured. The major weaknesses of OJT are 
that it often must take a back seat to production, and it is 
limited by production demands. Thurlow (25) listed several 
other limitations of OJT. 

1. The optimum sequence of training tasks cannot be ar- 
ranged without interfering with ongoing work. 

2. Some tasks as encountered on the job are too complex, 
fast-paced, or pressured to give an effective demonstration 
or practice opportunity for the trainee. 

3. The use of expensive equipment may be such an eco- 
nomic loss that it may be difficult to find opportunities for 
trainees to practice on the equipment. Trainees may then 
be assigned to semiskilled duties that do not interfere with 
the ongoing work, but also do not provide the planned train- 
ing opportunities. 

4. If the instructor is a production worker, attention to 
production demands interferes with his or her capacity to 
train. 

5. Generally, no diagnostic measures are available 
from OJT unless special provisions are made. Production 
records have distinct limitations as indexes of employee 
performance. 

The cost-benefit ratio of OJT may not compare favorably 
with off-production training sections. With training sec- 
tions, more trainees can be trained by a single instructor 
than is possible in a good OJT program. The cost of unstruc- 
tured OJT is low, but so are the results. The costs of struc- 
tured OJT programs are as high, or higher than when us- 
ing training sites and a small cadre of instructors. And, of 
course, there are greater dangers to life and property in- 
volved in OJT as compared to using training sections. 

Most mine training programs use several of these train- 
ing methods; the most common combination is probably 
classroom training, followed by OJT. 



DEVELOPING A TRAINING PROGRAM 

The development of a training program should be an 
orderly, logical process to insure that the training addresses 
the needs of the organization and meets the objectives set 
forth for the training program. This logical, orderly process 
is called instructional systems design (ISD) and has been 
used by the military and large corporations for many years 
to develop effective training programs. ISD is a series of 



interrelated activities. Although each application of ISD 
uses a slightly different set of activities, all have certain 
features in common. Figure 9-4 depicts an ISD approach 
to training development, and will serve as a model for 
discussion. All ISD methodologies start by assessing train- 
ing needs and writing training objectives. Somewhere in 
the process, criteria and evaluation measures are developed 
to assess the effectiveness of the training program. The 
training program is developed, evaluated, and revised based 
on objective performance data where appropriate. The 
following is a brief discussion of each box in figure 9-4. For 
a more complete discussion of the ISD approach, the reader 
is referred to Goldstein (10) or Tracey (26). 

Assess Training Needs 

A potential training need can be defined as the dif- 
ference between desired and actual performance. It must 
be stressed, however, that all such discrepancies may not 
be training related. In previous chapters, the importance 
of task and equipment design has been discussed, as have 
the effects of environment on human behavior. A discrep- 
ancy between desired and actual performance is often cor- 
rected more cost effectively through the application of 
human factors design criteria than through training. There- 
fore, in determining training needs, it is first necessary to 
identify where behavior is not meeting expectation, and 
then to determine the best course of action for reducing the 
discrepancy: whether by means of human factors design 
changes, training, or a combination of both. 

Assessing the difference between desired and actual per- 
formance requires that one know what is desired and what 
is the level of actual performance. In some cases, both types 
of information are collected separately and compared. For 
example, a standard or expectation may have been devel- 
oped that a particular maintenance job should take 2 h to 





Assess 
training needs 








1 








Write goals 
and objectives 




Determine criteria 

and evaluation 

measures 


















Select training 
modes and media 


















> 












Develop training 
materials 
















Revise 






! 








t 




Evaluate 












effect 


veness 









Figure 9-4.— Instructional system design approach to develop- 
ment of training programs. 



125 



complete; when, in fact, it is actually taking an average of 
4 h. In those cases where specific standards against which 
to compare performance do not exist, it is necessary to rely 
on expert judgment. For example, a maintenance supervisor 
would be asked if the performance of some of the mechanics 
needs to be improved. 

There are many sources of information that can be used 
to identify potential training needs, some of which are listed 
in table 9-2. It is usually best to use a variety of sources, 
as each one taps different aspects and populations. 

Table 9-2.— Sources of information for assessing training needs 



Opinions 



Statistics 



Performance 
measures. 



Supervisor round-table discussions. 

MSHA inspector discussion. 

Worker surveys and questionnaires 

Employee performance evaluations. 

Accident reports. 

MSHA inspector reports. 

Industry statistics. 

Absenteeism data. 

Maintenance records. 

Productivity records. 

Job skill tests. 

On-the-job observations. 

Paper-pencil tests of job knowledge and procedures. 



If used properly, accident data can be an excellent source 
of training needs information. First, it must be recognized 
that the data are incomplete; that is, many unsafe acts do 
not result in accidents and, hence, are not a part of the data 
base. Second, one must develop long-term trend informa- 
tion based on meaningful categories, so that slowly increas- 
ing trends can be identified. A tabulation of injuries by part 
of body may not reveal as much information as a tabula- 
tion of injuries by worker activity or type of accident. Safety 
directors often do not keep long-term trend data, except 
perhaps for total accidents; and they only identify a prob- 
lem when there is a rash of similar accidents over a short 
period of time. The slow buildup problems are often missed. 

Write Goals and Objectives 

Based on the assessment of training needs, the next step 
in the process is to write the goals and specific objectives 
of the training program. Goals are more comprehensive 
than objectives. Each goal will have a number of objectives 
associated with it. An effective, meaningful instructional 
objective should meet the following three criteria (28): 

1. Identify, as precisely as possible, what an individual 
will be doing to demonstrate that an objective has been 
reached. 

2. Describe the important conditions under which an in- 
dividual must demonstrate competence. 

3. Define the criteria or standard of acceptable perfor 
mance expected. 

Specific objectives serve several purposes. First, they 
help insure that both the instructor and the student under- 
stand what is to be gained from the training. Second, they 
focus the training on behaviors that are measurable. 

Some examples of specific behavioral training objectives 
include 

1. Given four dirty and two clean respirator filters, the 
student can pick out the four dirty filters. 

2. For each of the three types of respirators used in the 
mine, the student can list how often the filter must be 
checked and replaced. 



3. Given a type X respirator, the student can disassem- 
ble and replace the filter in less than 1 min. 

4. The student can identify each of the three types of 
respirators used in the mine and indicate what each pro- 
tects against. 

In writing objectives, it is critical to specify what is 
really important for the student to learn, rather than that 
which is easy to measure. For example, it may not be im- 
portant whether a person can name every part of a 
respirator, although this is easily determined. What may 
be more important is that the person can disassemble, in- 
spect, clean, and reassemble the respirator in a specified 
time. The latter objective is more difficult to measure, but 
may be the critical behavior that one wants to develop. 

Determine Criteria and Evaluation Measures 

Evaluation measures flow directly from the objectives 
and should be specified before the actual training materials 
and programs are designed. Training directors often develop 
the evaluation measures after they have developed the 
training course. The problem with this is that the evalua- 
tion measures may be based on the course content, which 
may or may not be designed to meet the training objectives. 
It is important to develop the evaluation measures direct- 
ly from the objectives so that they can be used to evaluate 
the training in determining if the objectives are being met. 
Evaluation measures can include paper-and-pencil tests, 
performance on a simulated task, on-the-job performance, 
supervisor ratings, and student opinion surveys. 



Select Training Modes and Media 

The type of training modes and media used depends in 
great part on what skill is being trained. Role playing, group 
discussion, and case study are effective in training atti- 
tudinal and decisionmaking skills. Simulators and on-the- 
job training are effective for training perceptual and motor 
skills. Movies and slides are effective for training percep- 
tual skills and job knowledge. The proper mix of modes and 
media must be carefully selected and should not merely be 
whatever is available. 

Develop Training Materials 

Training materials can be developed in-house, pur- 
chased from outside sources, or purchased from outside 
sources and tailored to the specific needs and problems of 
a particular mine. The Bureau's Pittsburgh (PA) Research 
Center has compiled an extensive list of commercially avail- 
able training materials appropriate to the mining industry 
that is available to individuals and companies. In-house 
development of materials includes slide presentations using 
actual people and areas of the mine to illustrate training 
points, videotapes of job procedures (7), posters summariz- 
ing key points, and models and mockups of equipment to 
demonstrate correct actions. 

Effective training materials should include short tests 
so that students and instructors can assess the progress be- 
ing made during a training program. The training should 
be divided into small modules so that students can digest 
one module before going on to the next. This also gives the 
student a sense of accomplishment when each module is suc- 
cessfully completed. 



126 



Evaluate Effectiveness 

The evaluation measures, developed from the training 
objectives, are used to test the trainees and assess whether 
the training objectives were met. In addition, other evalu- 
tion data are collected. Student opinions should be solicited; 
they are an excellent source of data on how a training pro- 
gram could be improved. Followup on the job is critical. 
Training personnel should seek supervisor opinions as to 
whether training has improved job performance and what 
areas need to be stressed further in training. Accident, pro- 
duction, and maintenance records should be reviewed to 
assess any positive impact of the training. 

Revise 

Based on the evaluation data, changes are made to the 
modes, media, and content of training programs. Objectives 
should not be revised based on the evaluation; they should 
be revised based on a reassessment of training needs. Every 
training program will need to be revised at some time. 
Materials go out of date, training needs change, and the 
types of students change. All of these necessitate the con- 
stant review and revision of a training program. 



SAFETY AWARENESS PROGRAMS 

Safety awareness programs typically include various 
communications, promotional devices, and contests aimed 
at increasing employee awareness of the importance of 
working safely. Probably one of the most extensive aware- 
ness programs is that undertaken by Consolidation Coal 
Co. (2). The following sections briefly describe this program 
and summarize the elements that contributed to its success. 

Consol's Program 

The Consol program was a four-pronged approach. It in- 
volved (1) establishment of a corporate-wide safety depart- 
ment and corresponding departments in each operational 
region, (2) an intensive safety training program, (3) an all- 
out safety engineering program, and (4) a safety communica- 
tions program to heighten awareness among all employees. 

A symbol (the A-OK hand signal: with index finger and 
thumb forming a zero) and a slogan (Consol's Goal— Zero 
Accidents) were selected and used consistently on all com- 
munication and promotional materials. It was recognized 
that to be effective, both the workers and their families had 
to be involved. Family involvement was accomplished by 
sending a quarterly safety newsletter to the families. In 
addition, all sorts of promotional items were mailed to the 
homes, including packets of sugar, salt, mustard, ketchup, 
baggies, and handy wipes— all with the symbol and slogan 
printed on them— to be packed in lunchboxes as reminders. 
Potholders, Christmas wrappings, and toboggans were 
given away, again all emblazoned with the safety symbol 
and slogan. To keep the link between job safety and family 
salient, safety posters were displayed at the mines with pic- 
tures of employees' children and messages such as, "Dad, 
work safely so you can give me away at my wedding" or 
"Work safe, Dad, we need you at home." 

In addition, the workers were also given safety slogan 
items to maintain their awareness of the program, including 
fishing knives, leg bands, belt buckles, caps, and retroreflec- 
tive stickers for their helmets. Paycheck stuffers were in- 



cluded to promote specific safety concerns. Extensive 
signage was used at the minesites, including safety clocks 
and thermometers. Even the jumpsuits of the mine rescue 
teams had the safety symbol and slogan on them. 

To complement the communications, safety awards were 
given. Workers earned points for safe work performance and 
could use them to purchase gifts. Jackets and caps were used 
regionally to reward a good safety record. Gold pins were 
given to superintendents whose operations had no lost-time 
accidents for a year, and safety trophies were given to opera- 
tions with 1 million work-hours without an accident. 

In 1978 it was reported that the program was costing 
approximately $200,000 per year, but during the first 6 yr 
of the program, the accident frequency rate was reduced 
by almost 60%. 

Elements of a Successful Program 

There are several aspects of the Consol program that 
accounted for its success. These elements have also been 
found to be essential for such programs in other industries 
as well. First, and perhaps foremost, is top management's 
total commitment to the program. Second, an awareness 
program must be part of a larger safety program, with 
strong emphasis on training and engineering-human fac- 
tors approaches to accident reduction. Third, it is impor- 
tant that the worker's family is made an integral part of 
the awareness program. It has also been suggested that the 
community be included. Fourth, a wide variety of devices 
must be used to get the message across. Safety slogan items 
must be changed periodically, and new items must be in- 
troduced to keep interest high. The prizes and gifts must 
be updated and expanded. 

It is impossible to determine which specific aspects of 
the Consol program were effective and which were not. In 
all likelihood, it was the totality of the program that was 
effective. It is much like analyzing how a dam holds back 
water. Examining each individual stone would lead to the 
conclusion that each stone, by itself, would not hold back 
the water, yet all the stones together hold back the water 
very effectively. 

Safety Signs 

Unfortunately, many companies rely on safety signs as 
their primary method of increasing safety awareness. There 
are some characteristics of effective signs that are worth 
pointing out, in addition to those dealing with such issues 
as attention-getting, visibility, and comprehensibility. 

First, safety signs must reinforce other aspects of a com- 
pany's safety program. Signs should correspond to aspects 
being stressed in training or at weekly safety meetings. In 
essence, signs should be part of a focused campaign aimed 
at a select number of safety problems. For example, signs 
may be directed toward the use of lockouts in electrical 
maintenance work. The message would be stressed by super- 
visors on the job and in safety meetings, better lockout 
designs would be installed, new job procedures developed, 
etc. 

Second, the signs should be directed to specific safety 
problems rather than general messages. The emphasis 
should be on what to do. rather than just what not to do. 
(Note that the Consol program used general be-safe type 
signs; by themselves, they probably would not have been 
very effective.) Signs showing specific actions are usually 
more effective. It is usually agreed that, where possible, the 



127 



consequences of not performing the action should be illus- 
trated on the sign. For example, if the message on a sign 
was to block the wheels of vehicles parked on an incline, 
the sign might also show a runaway vehicle hitting a 
person. 

Third, signs should be placed where they are needed. 
A block-the-wheels sign, for example, should be hung on 
inclined roadways where vehicles are likely to be parked, 
and on the vehicles themselves. It would do little good to 
hang them in the clean room or lunch area. Related to the 
place-them-where-you-need-them principle is that one 
should not overdo the placement of signs. If there are safety 
signs everywhere a worker looks, the signs may quickly lose 
their significance and be ignored. 



DISCUSSION 

This chapter has reviewed training and similar 
endeavors as they relate to the achievement of organiza- 
tional goals— increased safety and productivity. The chapter 
is not meant to be a how-to guide for developing training 
programs, but rather as a survey of the utility, methods, 
and lessons learned from the field. 

Training often aims at redirecting and increasing moti- 
vation. Chapter 10 deals with the topics of motivation and 
organizational development which can be viewed as a 
logical extension of the training function to embrace the 
entire organization and the interactions of its parts. 



REFERENCES 

1. Adkins, J., R. Akeley, P. Chase, L. Marrus, W. Prince, R. 
Rodick, C. Rogne, J. Saalberg, and L. Szempruch. Review and 
Evaluation of Current Training Programs Found in Various Min- 
ing Environments. Volume I, Summary (contract S0144010, Ben- 
dix Corp.). BuMines OFR 110(l)-76, 1976, 67 pp.; NTIS PB 259 410. 

2. Cochran, H. Safety Communications for Reducing Mine Ac- 
cidents. Min. Congr. J., v. 64, No. 6, 1978, pp. 27-29. 

3. Cohen, A. Factors in Successful Occupational Safety Programs. 
J. Safety Res., v. 9, 1977, pp. 168-178. 

4. Cohen, A., M. Smith, and H. Cohen. Safety Program Practices 
in High Versus Low Accident Rate Companies: An Interim Report 
(Questionnaire Phase). NIOSH, Cincinnati, OH, DHHS 75-185, 
1975, 183 pp.; NTIS PB 298-332. 

5. Cohen, H., and R. Jensen. Measuring the Effectiveness of an 
Industrial Lift Truck Safety Training Program. J. Safety Res., v. 
15, No. 3, 984, pp. 125-135. 

6. Couillard, D.T., and B.C. Nelson. Task Training in the Iron 
Mining Industry: Two Approaches. BuMines IC 8994, 1984, 11 pp. 

7. Couillard, D.T., B.C. Nelson, and R.R. Tomassoni. Video- 
Supplemented Task Training at the United States Steel Corp. 
Minntac Mine, Mt. Iron, MN. BuMines IC 8999, 1985, 9 pp. 

8. Davis, R.T. and R.W. Stahl. Safety Organization and Activities 
of Award-Winning Companies in the Coal-Mining Industry. 
BuMines IC 8224, 1964, 26 pp. 

9. Digman, R.M., and J.T. Grasso. An Observational Study of 
Classroom Health and Safety Training in Coal Mining (contract 
J0188069, WV Univ.). BuMines OFR 99-83, 1982, 65 pp.; NTIS PB 
83-210518. 

10. Goldstein, I. Training: Program Development and Evalua- 
tion. Brooks and Cole, 1974, 229 pp. 



11. Hardy, K. Training With OBSAC. Paper in Proceedings of 
TRAM 10 (Training Resources Applied to Mining), PA State Univ., 
Aug. 14-17, 1983, pp. 46-52. 

12. Hoover, R. Cumberland Training Center and Simulated Mine. 
Min. Congr. J., v. 65, 1979, pp. 46-48. 

13. Komaki, J., K. Barwick, and L. Scott. A Behavioral Approach 
to Occupational Safety. J. Appl. Psych., v. 63, 1978, pp. 434-445. 

14. Komaki, J., A. Heinzmann, and L. Lawson. Effect of Train- 
ing and Feedback: Component Analysis of a Behavioral Safety Pro- 
gram. J. Appl. Psych., v. 65, 1980, pp. 261-270. 

15. Krupp, K., and J. Applegate. Haulage Truck Training System 
(contract J0387221, Woodward Assoc. Inc.). BuMines OFR 61-85, 
1983, 224 pp.; NTIS PB 85-215762. 

16. McAteer, J., and L. Galloway. A Comparative Study of Miners' 
Training and Supervisory Certification in the Coal Mines of Great 
Britain, The Federal Republic of Germany, Poland, Romania, 
France, Australia and the United States: The Case for Federal Cer- 
tification of Supervisors and Increased Training of Miners. WV Law 
Rev., v. 82, 1980, pp. 936-1016. 

17. McGrath, J. Aggressive Safety Skills Training Gets Results 
at Illinois Coal Mine. Mine Safety and Health, Spring-Summer, 
1983, pp. 2-9. 

18. Menzer, G, J. Curtin, and F. Bick. A Training Analysis Ap- 
proach to the Education of Coal Miners. McDonnell Douglas 
Astronautics Co., St. Louis, MO, MDC-E-1566, 1976, 145 pp. 

19. Morris, C.W., and E. Conklin. Development and Fabrication 
of a Continuous Miner Training System. Volume 2 (contract 
H0377024, McDonnell Douglas Electronics Co.). BuMines OFR 
140(2)-83, 1982, 79 pp. 

20. National Academy of Sciences. Toward Safer Underground 
Coal Mines. 1982, 190 pp. 

21. Peay, J., W. Wiehagen, and G. Bockosh. The Human Element 
in Mining— An Overview of Bureau of Mines Human Factors 
Research. Paper in Proceedings of the 15th Annual Institute on 
Coal Mine Health, Safety and Research, Aug. 28-30, 1984. VA 
Polytechnic and State Univ., Blacksburg, VA, 1984, pp. 61-83. 

22. Robertson, N. What Does Research Tell Us About Training? 
Pres. at Assoc, of Mine Managers Meeting. Chamber of Mines, 
Johannesburg, South Africa, February 1979, 12 pp.; available upon 
request from M.S. Sanders, Essex Corp., Westlake Village, CA. 

23. Seidle, N. Shuttle Car Operator Training System (contract 
H0272039, ORI Inc.). BuMines OFR 59-85, 1984, 84 pp.; NTIS PB 
85-215788. 

24. Short, J., J. Harris, J. Waldo, and S. Barber. A Study to Deter- 
mine the Manpower and Training Needs of the Coal Mining In- 
dustry (contract J0395038, John Short and Assoc). BuMines OFR 
14-80, 1979, 145 pp.; NTIS PB 80-164742. 

25. Thurlow, R., J. Olmstead, and R. Trexler. On-The-Job Train- 
ing and Social Learning Theory: A Literature Review. Human 
Resour. Res. Organization Inc., Alexandria, VA, 1980, 56 pp. 

26. Tracey, W. Designing Training and Development Systems. 
Am. Management Assoc, 1971, 432 pp. 

27. Uslan, S.S., H.M. Adelman, and R.S. Keller. Testing the Ef- 
fects of Applied Behavioral Analysis and Applied Behavioral 
Management Techniques on the Safe Behaviors of Salt Mine Per- 
sonnel (contract J0166137, Salt Inst.). BuMines OFR 44-80, 1978, 
41 pp.; NTIS PB 80-171309. 

28. U.S. Occupational Safety and Health Administration 
(Washington, DC). Training Guidelines: Request for Comments and 
Information. OSHA 76-135, 1976, 11 pp. 

29. Wiehagen, W. Current Research in the Application of Train- 
ing Equipment Supporting Equipment Operator Training. Paper 
in Mine Safety Education and Training Seminar Proceedings: 
Bureau of Mines Technology Transfer Seminars, Pittsburgh, Pa.. 
Dec. 9, 1980; Springfield, 111., Dec. 12, 1980; and Reno, Nev., Dec. 
16, 1980; comp. by Staff— Pittsburgh Research Center. BuMines 
IC 8858, 1981, pp. 46-58. 



128 



CHAPTER 10.— MOTIVATION AND ORGANIZATIONAL DEVELOPMENT 




The link between organizational climate and safety and productivity has become apparent. Work organiza- 
tion concepts of bygone days are now only seen in photographs found in the National Archives. 



Throughout this report, the effects of equipment and 
environment on human behavior have been emphasized. 
The topics have been rather technical, with a definite 
engineering flavor. The importance of motivation has been 
occasionally alluded to as a determinant of performance, 
but it has not been discussed in depth; that is the purpose 
of this chapter. 

Chapter 8 discussed environmental factors, including 
illumination, noise, vibration, and heat, that influence 
behavior. In this chapter another environmental factor in- 
fluencing behavior— organizational climate— will be dis- 
cussed. The effects of organizational climate on behavior 
are more psychological in nature than are the effects of the 
factors discussed in chapter 8. In keeping with the emphasis 
on changing the job to fit the person, this chapter will pre- 
sent the process of organizational development, and specific 
attempts made to alter the organizational climate in the 
mining industry. 



MOTIVATION 

The term "motivation" is rather loosely used to describe 
the drive, thrust, or energy behind an individual's behavior. 
In addition, a goal-oriented function of motivation is in- 
ferred. People are not just motivated; they are motivated 
to do something or obtain something. Motivation, then, is 
responsible for the intensity, direction, and persistence of 
behavior. 



Motivation and Performance 

Motivation is related to performance, but it is not the 
same thing as performance. Performance is a function of 
ability and motivation. Many theories suggest the follow- 
ing equation to express this relationship: 

Performance = /"(ability x motivation). 

The multiplicative relationship is important and implies 
that, if either motivation or ability are zero, performance 
will be zero. In essence, all the motivation in the world will 
not yield satisfactory performance unless a person has the 
ability to perform satisfactorily. The converse is also true: 
a person with all the ability in the world will not perform 
without the motivation to do so. 

Ability refers to how well a person can perform at a 
given time. As such, ability is considered to be a function 
of aptitude, training, and experience. Thus 

Ability = /"[aptitude x (training + experience^]. 

Aptitude is an enduring, inalterable quality of an in- 
dividual that imposes a fixed limit on his or her level of 
potential performance. As such, aptitude determines 
whether an individual can be brought through training 
and/or experience to a specified level of performance. Notice, 
this expression implies that without aptitude, all the train- 
ing and experience will not give an individual the ability 
to perform. 



* 



129 



One important implication of all this is that not all per- 
formance problems that occur in organizations are caused 
by low motivation. Problems can be caused by low aptitude; 
inadequate training and experience; or poorly designed jobs, 
equipment, and environments that exceed whatever abili- 
ties people may have. 



Motivation and Needs 

For centuries, psychologists and philosophers have tried 
to explain why some objects or outcomes seem to be desired 
by people, while others are not. People have needs; and it 
is assumed that if these needs are better understood, a bet- 
ter understanding of why people act as they do follows. 

There have been many attempts to classify human 
needs. Probably the most influential theory of human needs, 
and by far the most widely used classification system for 
the study of motivation in organizations, is the hierarchical 
classification scheme of Maslow {11-13)} He postulates five 
categories of needs as follows: 

1. Physiological needs, including the need for food, water, 
air, etc. 

2. Safety needs, including the need for security, stabil- 
ity, and the absence from pain, threat, or illness. 

3. Belongingness and love needs, which include the need 
for affection, fellowship, love, etc. 

4. Esteem needs, including both the need for personal 
feelings of achievement or self-esteem, and the need for 
recognition or respect from others. 

5. The need for self-actualization, that is, the feeling of 
self-fulfillment or the realization of one's potential. 

According to Maslow, these five needs categories exist 
in a hierarchy of importance, such that the lower or more 
basic needs (physiological, safety) are inherently more im- 
portant than the higher needs. This means that, before any 
of the higher level needs will become important, a person's 
physiological needs must be satisfied. Once the physiological 
needs have been satisfied, their strength or importance 
decreases, and the next higher-level need becomes the 
strongest motivator of behavior. At the highest level of the 
hierarchy, a slightly different thing occurs. For self- 
actualization, increased satisfaction of the need leads to in- 
creased need strength. The more you get, the more you 
want— but, according to Maslow, this only occurs at the top- 
level need. 

Maslow does say that the hierarchy is not rigidly fixed 
for all people. He clearly states that physiological needs are 
at the bottom, and self-actualization needs are at the top; 
but the order of the middle needs may vary from person to 
person. 

This theory suggests, for example, that as people are 
promoted and their lower-level needs become satisfied, they 
will become more concerned with self-actualization and 
growth. If these higher order needs are not addressed, peo- 
ple may become dissatisfied with their jobs. The theory also 
suggests that if a person's job security is threatened, that 
person will abandon all else in order to protect it. 

Maslow, however, is not the last word on needs theories. 
Some theorists take exception to parts of his theory because 
the empirical evidence has not always supported it. Some 
believe that there are fewer levels of needs, that all can be 
o' erating at the same time, and that failure to satisfy a 



1 Italic numbers in parentheses refer to items in the list of references at 
the end of this chapter. 



higher order need can cause a lower order need to increase 
in importance. 



A Theory of Motivation 

Theories of human needs, such as that of Maslow, are 
useful for explaining what outcomes will be attractive to 
an individual; but they are not sufficient to explain the in- 
dividual's behavior. The reason is that such theories do not 
include many of the factors that are known to influence 
motivation. There have been numerous theories of motiva- 
tion over the years, but one has attracted considerable at- 
tention and research support in the work environment; i.e., 
expectancy theory (16). 

Expectancy theory states that people will expend effort 
(motivation) toward a performance goal if they perceive that 
their efforts will result in attaining that level of perfor- 
mance, and the attainment of that level of performance will 
lead to desired outcomes. The theory utilizes three main 
concepts: valence, effort-performance expectancy, and 
performance-outcome expectancy. Each of these are ex- 
plained, in reference to figure 10-1 (10), in the following 
sections. 

Valence 

The valence of an outcome refers to the affective 
response of a person to an outcome. An outcome can have 
a positive valence, in which case the outcome is something 
a person desires or wishes to attain; a neutral valence, as 
when a person is indifferent to the outcome; or a negative 
valence, as when a person prefers not to attain the outcome. 
Examples of outcomes include a pay raise, working with 
a friend, losing one's job, working in less hazardous and 
more pleasant surroundings, being praised by one's super- 
visor, gaining a sense of accomplishment, being ostracized 
from a group, being injured, etc. 

Effort-Performance (E-P) Expectancy 

E-P expectancy is simply a person's estimate, in a given 
situation, of the probability that he or she will attain a 
performance level if he or she puts in the effort. Figure 10-1 
shows two levels of performance, satisfactory and unsatis- 
factory; but these could also represent alternative perfor- 
mances, such as doing the job safely and unsafely. 

Performance-Outcome (P-O) Expectancy 

P-0 expectancy is the perceived probability that a level 
of performance will lead to an outcome. Some outcomes are 
certain to follow from performance, such as a feeling of 
accomplishment when a difficult task is satisfactorily com- 
pleted. Some outcomes will occur, regardless of the perfor- 
mance level attained (e.g., outcome C in figure 10-1). Other 
outcomes may or may not occur, depending on the situation. 

The Model 

Expectancy theory postulates that for each outcome that 
can result from a level of performance, people multiply the 
P-0 expectancy by the valence (V). These are summed for 
all the outcomes attached to a performance level to obtain 
an overall valence for the performance level. This overall 



130 



Outcome 
B 



Expectancy 




Performance 
A 



Outcome 
B 



Performance 
B 



KEY 

Performance 

A The intended performance, a 
successful result from effort 

B Performance other than that intended, 
an unsuccessful result from effort 




Outcome 




Outcome 



Outcome 



Outcome 



Outcome 
B 



Outcome 
B 




Outcome 



Outcome 

A An outcome sought as an end in itself 

B An outcome sought as a prerequisite to other outcomes 

C An outcome that can be obtained whether or not the 
effort leads to the intended performance 

Figure 10-1.— Schematic representation of expectancy theory of motivation (10). (Courtesy of Brooks and Cote) 



valence is then multiplied by the E-P expectancy to deter- 
mine the level of motivation a person will experience toward 
attaining the performance level. This is done for various 
performance levels, and the level of performance with the 
highest motivation level is the one that a person, in theory, 
will choose to attain. In formula format: 

Motivation = (E-P) x [(P-O) x (V)]. 

There are several implications of this model. People will 
not pursue a performance if it is perceived that the attain- 
ment of the performance will result in a net negative overall 
valence, unless all other performance levels will result in 
even more negative valences. Attaining a high level of pro- 
ductivity may get the praise of a supervisor and maybe even 
a promotion, but it may also result in the loss of friends 
and being overly fatigued at the end of the day. Depending 
on the P-0 expectancy and valence of each of these, the 
overall valence could be positive or negative. On a smaller 
scale, wearing safety glasses may result in fewer injuries 
(positive valence), but it can also result in discomfort and 
lower visual ability due to fogging (negative valence). 
Whether people wear saftey glasses depends on their P-0 
expectancies and valences for these and other outcomes. 



Implications of the Model 

Table 10-1 lists the major factors that influence E-P and 
P-0 expectancies. People often have an inaccurate percep- 
tion of a situation, which can lead to incorrect P-0 or E-P 
expectancies. They may not understand the high probability 
of an accident if certain unsafe procedures are followed, or 
they may perceive that the safe way of doing a job is more 
difficult or time consuming than an unsafe way. Proper 
training can often correct such misconceptions. Training 
can also alter E-P expectancies by increasing a person's self- 
esteem and ability to perform the work. The way a work 
group and supervisor reward performance also affects the 
P-0 expectancies. If safe behavior is rewarded, then the P- 
O expectancy for that outcome increases. If a person is 
criticized for reduced production because he or she chose 
to use a safe job procedure, P-0 expectancies will also be 
affected. 

P-0 expectancies are influenced by the valence of the 
outcomes themselves. To most people, positive outcomes are 
believed more likely to occur than negative outcomes. Peo- 
ple also tend to discount the possibility that very negative 
things (e.g., injury or death) will happen to them. Is it any 
wonder that people will engage in behaviors that will save 



131 



Table 10-1 .—Factors that influence performance-outcome (P-O) 
and effort-performance (E-P) expectancies (10) 

(Reprinted with permission by Brooks and Cole) 



E-P 



P-O. 



Self-esteem 

Past experiences in similar situations. 

Actual situations. 

Communications from others. 

Past experiences in similar situations. 

Attractiveness of outcomes. 

Belief in self versus fate. 

Actual situations. 

Communications from others. 



a little time (positive valence and high P-O expectancy), but 
will expose them to danger of bodily harm (high negative 
valence, but low P-O expectancy). 

One goal of mine management, then, should be to struc- 
ture a situation so that positively valenced outcomes occur 
when desirable behaviors are performed, and that either 
negatively valenced outcomes occur when undesirable 
behaviors occur; or, at the least, positively valenced out- 
comes do not occur. In addition, training should be aimed 
at reinforcing the connection between performance and out- 
come, and at increasing the expectancy that the perfor- 
mance desired will be attained if effort is expended. 



ORGANIZATIONAL CLIMATE 

Organizational climate refers to the collective percep- 
tions held by employees about aspects of their organiza- 
tional environments. These perceptions have a psycholog- 
ical utility in serving as a frame of reference for guiding 
appropriate and adaptive task behaviors. Perceptions that 
make up organizational climate include whether manage- 
ment is perceived as caring about the individual workers; 
whether management listens to workers' suggestions and 
complaints; whether productivity is stressed more or less 
than safety; whether the coworkers support one another and 
work together, etc. 

An important component of organizational climate that 
he called safety climate or the concern for safety was 
distinguished by Zohar (18). Organizational climate, in- 
cluding safety climate, is assessed by the use of question- 
naires administered to employees of a company. Usually, 
a rating form is used to solicit perceptions on specific dimen- 
sions. Zohar, for example, used a 49-item questionnaire to 
measure safety climate, in which employees marked a 
5-point scale for each item (strongly disagree-disagree- 
neutral-agree-strongly agree). The questionnaire tapped 
the following perceptions: 

Perceived importance of safety training programs. 

Perceived management attitudes toward safety. 

Perceived effects of safe conduct on promotion. 

Perceived level of risk at workplace. 

Perceived effects of required work pace on safety. 

Perceived status of safety officer. 

Perceived effects of safe conduct on social status. 

Perceived status of safety committee. 
Zohar also found strong correlations between the scores 
on the safety climate questionnaire and the rankings by 
safety inspectors of the overall safety records of 50 
companies. 

One of the first studies to investigate the relationship 
between organizational climate and accidents in the mining 
industry was carried out by Sanders (15). Miners from 22 
underground coal mines were administered questionnaires 



that examined their perceptions of such things as decision 
decentralization, shared autonomy, management receptive- 
ness, production pressure, feedback, management support - 
iveness and concern for working conditions, and worker 
morale. 

Using a sophisticated cross-lagged correlational design 
that required testing at each mine approximately 6 months 
apart, the following conclusions were made based on the 
data: 

1. When decisions are decentralized, when management 
is flexible and innovative in trying new procedures and pro- 
grams, and when morale is high, disabling injuries decrease. 

2. As disabling injuries increase, feedback, continued 
employee development, and consistency of orders improve. 
That, in turn, appears to decrease injuries. 

3. Production pressure appears to lead to an increase in 
disabling injuries. The increase in disabling injuries, in 
turn, leads to a decrease in production pressure. 

A basic conclusion from this study was that certain 
organizational climate and managerial practices affect in- 
jury rates; and, further, that injury experiences have an 
effect on other climate and managerial issues. Therefore, 
in order to reduce accidents, one must not only focus on the 
worker and the physical environments, but must also focus 
on the broader organizational context and managerial prac- 
tices within which the miner works. The techniques used 
to change the broader organizational context and mana- 
gerial practices are in the province of organizational 
development. 



ORGANIZATIONAL DEVELOPMENT 



Organizational development (OD) is a long-term effort 
that examines and alters management policies, practices, 
and organizational dynamics in a systematic way for the 
purpose of assisting a company to solve its major problems 
and to achieve its major goals (1). OD recognizes that the 
key unit in an OD activity is the ongoing work team, in- 
cluding both the supervisor and his or her subordinates. 
This is in contrast to the more traditional management 
development approach that concentrates on the individual 
managers and supervisors, rather than on the intact work 
groups. 

Another distinguishing feature of OD is the use of a 
change agent to initiate and guide the OD activity. The 
change agent is a third party, external to the particular part 
of an organization that is initiating the OD activity. This 
change agent usually does not make recommendations in 
the traditional sense, but rather intervenes in the ongoing 
processes of the organization, and assists the organization 
in understanding and changing how it goes about solving 
problems. 

A final distinguishing characteristic of OD is that the 
activities generally follow an action research model. Basi- 
cally, an action research model consists of (1) a preliminary 
diagnosis of an organization's (or work group's) problem, 
(2) data gathering from the group to further diagnose the 
source of its problems, (3) data feedback to the group that 
summarizes the findings from the data gathering, (4) discus- 
sion by the group of the findings, (5) action planning by the 
group to solve the problems uncovered, (6) implementation 
of the action plan, and (7) monitoring and evaluating the 
action plan to insure that the problems are indeed being 
solved. 



132 



Actually, OD is more of a philosophy than a specific 
methodology. OD activities take many different forms. To 
provide an appreciation for OD, four OD projects that were 
carried out in the mining industry will be reviewed: the 
Rushton autonomous work group experiment, the Hecla 
team-building project, the Texasgulf leader-match study, 
and the use of quality circles by mining companies. 

Rushton Autonomous Work Group Experiment 

This project began in 1974 and was sponsored by the 
Department of Commerce and the Ford Foundation. I' 
represents probably the most comprehensive OD activity 
initiated in the coal industry. The implementation and 
results are fully detailed by Goodman (7). The Rushton 
experiment was and is one of the more controversial OD 
interventions, perhaps because of the extensive attention 
it generated (3, 14, 1 7) and the problems it encountered. 

Background 

The Rushton Mine was owned by Pennsylvania Mines 
Corp., which was part of Pennsylvania Power and Light. 
The mine was located in central Pennsylvania and em- 
ployed about 200 people. The workers were members of the 
United Mine Workers of America (UM WA). The project can 
be considered as being composed of two phases. The first 
phase involved the OD intervention on three shifts (each 
composed of eight-person crews) in one of the four working 
sections of the mine. The second phase involved efforts to 
expand the intervention to the other three working sections. 

Autonomous Work Groups 

The OD intervention involved setting up autonomous 
work groups. Basically, the miners in a crew organized and 
managed themselves. They performed all the different 
tasks, traded individual job assignments periodically, and 
learned all work conditions. Specifically, authority for daily 
production decisions was delegated to the mining crew. The 
foreman's job was to concentrate on safety, planning, and 
coordinating activities (not on daily production decisions). 
Key features of the plan were that each member of the crew 
was to learn all other jobs in the section, and all the mem- 
bers of the crew would receive the same top rate of pay. Fur- 
ther, two additional workers were added to each crew to 
do support work. 

A joint labor-management committee, consisting of five 
members from the union and five members from manage- 
ment, was to supervise the day-to-day project activities. All 
grievances were to go to the joint committee prior to going 
through the traditional grievance procedure. In addition to 
these efforts, an extensive training program was instituted, 
and a gain-sharing plan (like a profit-sharing plan) was to 
be instituted. This plan, however, was never implemented. 
The training consisted of classroom training, 2 full days per 
week for 3 weeks, covering the autonomous work group con- 
cept, reviewing all job tasks, job safety analysis, and Federal 
safety laws. Other changes, such as the introduction of dif- 
ferent performance appraisal systems and department-wide 
conferences, were also included. 

Results 

For the better part of 2 yr, the program worked well. 
The crews organized and solved problems collectively. In- 



formal leaders emerged and took over, while the foremen 
devoted their time to safety measures. 

The following are some quotes from the miners involved 
during the period of the experiment: 

Well, you're your own boss. You got your section 

and run things our own way and talk things over 

when you have to. 

Before, when a timber was down, you'd say the 

hell with it. Now you do something— it's your section. 

If something's wrong, we fix it now. 

We see that the work gets done, that the safety 

law is kept up. We learn how to run all the equipment. 

You want to come to work now. We all work together, 

like a team. 

But, fellow workers who were not involved in the pro- 
gram called them the Communist crews. They were envious 
of the freedom, flexibility, and higher pay of the experimen- 
tal sections. The jealousy and suspicion among the other 
miners at Rushton caused the UMWA local to withdraw 
its support by a narrow vote in 1977. 

Management went ahead with a modified version of the 
program and tried to expand it to other working sections. 
Lacking the support of the union, mine officials found it 
hard to gain the same spirit of cooperation from the mines. 
Miners who did not take part in the original experiment 
balked at taking the initiative in making decisions regard- 
ing their work. The foremen again took over the sections, 
and again had the dual and sometimes conflicting respon- 
sibilities for safety and production. 

Although productivity did not shoot up as anticipated, 
it did increase 3%. Job attitudes and safety, as measured 
by the number of safety violations and inspectors' ratings, 
shifted in a positive direction. However, accident rates 
showed little, if any, change due to the intervention; but 
they were low even before the experiment began. The level 
of job skills in the workforce definitely increased; and, at 
least among the miners involved in the experiment, a 
greater sense of teamwork developed. Both the management 
and the union felt that the project led to improved attitudes 
toward each other; and these attitudes probably facilitated 
the process of labor-management relationships during that 
period. 

HecJa Team-Building Project 

During the period of March 1980 through May 1982, 
the Bureau funded a demonstration project at the Hecla 
Mining Co. Lucky Friday Mine, located in the Coeur 
d'Alene region of northeastern Idaho (4). The purpose of that 
project was to investigate the feasibility and effectiveness 
of OD activities for the mining industry. The overall con- 
tract consisted of the Hecla project and the Texasgulf proj- 
ect (which will be discussed in a subsequent section). 

The OD activities at the Lucky Friday Mine primarily 
consisted of team-building and problem-solving activities, 
as well as the necessary skills training required to support 
those activities. A brief overview of the procedures used and 
the results obtained at the Lucky Friday Mine is presented, 
drawing heavily from Fiedler (4). 

Background 

The Lucky Friday Mine was a deep-vein, hard-rock mine 
(silver and lead), employing about 270 miners represented 
by the United Steelworkers of America. A comparison or 
control mine, at which no OD interventions were made, was 



133 



also included in the study. The comparison mine was the 
Star Mine, also owned by Hecla Mining Co. and located 
within a few miles of the Lucky Friday Mine. The Star Mine 
employed about 360 nonunion miners. The safety records 
of both mines were considered to be poor. 

As is so often the case in field research, anything that 
could go wrong did. During the intervention period, silver 
prices increased 800% and then fell dramatically. Also dur- 
ing the period, the Lucky Friday Mine experienced a 9-week 
work stoppage that made assessment of the impact of the 
OD intervention difficult. 

Team Building 

The primary intervention was through team-building 
and problem-solving meetings in which a boss and his or 
her immediate subordinates identified and resolved major 
problems to make their unit more effective. Some of the 
assumptions that underlie team building are (1) work teams 
are the basic building blocks of an organization; (2) effec- 
tive team functioning requires good leader-member rela- 
tions, clear team goals, clarification of role expectations, 
and individual and group problem-solving skills; (3) teams 
can improve their performance by systematically solving 
the major problems that confront them; and (4) enhancing 
work team performance makes individuals more competent 
and organizations more successful. 

The classic or team-building, problem-solving approach 
introduced at Hecla was governed by several principles. 

1. Start team building, problem solving at the top of the 
organization and work through all levels. 

2. Focus attention on intact work teams consisting of 
superiors and subordinates. 

3. Focus on getting the job done; that is, find better ways 
to accomplish the team's mission by solving major problems 
and seizing opportunities. 

4. Be data based; that is, discover problems, oppor- 
tunities, and solutions through fact-finding and diagnostic 
procedures. 

5. Be interaction oriented; i.e., develop and implement 
action plans to cause desired changes. Follow up and 
evaluate actions to ensure a general team-building, 
problem-solving framework, but use additional OD tech- 
niques as they are appropriate. 

The technique of team building involved a series of 
meetings in which high-priority issues facing the team were 
systematically examined and resolved. These meetings 
usually were conducted with the aid of a consultant who 
acted as a facilitator. Problems were defined and clarified, 
alternative solutions were evaluated, preferred solutions 
were implemented, and the effects of actions were monitored 
for desired results. Team building had two expected out- 
comes: the team's mission would be better accomplished, 
and working relationships among team members would be 
improved. 

Five, day-long, team-building meetings with the presi- 
dent and staff led to a formal statement of company philos- 
ophy and goals. An agreement on corporate strategy related 
to safety and productivity was developed. A statement of 
each department's goals, functions, responsibilities, and 
authority was also drawn up. 

Team-building meetings were held with the top-manage- 
ment team at the Lucky Friday Mine, as well as with the 
operations team that included the shift bosses. These 
meetings involved the mine manager, mine superintendent, 
mine foremen, shift bosses, and auxiliary support super- 



visors. These meetings dealt more intensively with issues 
of organizational coordination, communication, and coopera- 
tion. For example, support units were not delivering the 
needed services; some individuals and work units were not 
meeting others' expectations of what they should be ac- 
complishing. The outcomes of these meetings were improved 
methods for getting the job done and detailed strategies for 
reducing mine accidents and injuries. 

During the last phase of the project, team-building 
meetings were held with shift bosses and their work crews. 
The meetings addressed four main questions: 

1. What is preventing us from doing the job in the way 
we think it ought to be done? 

2. What are we doing that helps us get the job done? 

3. How can we get the job done more safely? 

4. How can be make this a better place to work? 



Performance Appraisal System 

The development of a reliable and acceptable perfor- 
mance evaluation system became the first accomplishment 
of the project. This was essential for several reasons. First, 
supervisors and managers needed feedback on the way in 
which their own supervisors viewed their effectiveness in 
dealing with production and safety problems. Second, an 
appropriate performance system focused attention on the 
areas of performance seen by management as important. 
Thus, including safety as one of the prominent areas in 
which supervisors and managers were judged had an almost 
immediate effect on the emphasis lower level managers 
placed on safety-related issues. Third, the project itself re- 
quired data that would reflect changes in performance in 
safety-related areas. The performance appraisal consisted 
of three evaluation forms (one for managers, one for pro- 
fessional and technical employees, and one for clerical per- 
sonnel) based on a key traits and behaviors format. 



Safety Activities 

The OD project activities at Hecla included a review and 
critique of Hecla's 40-h safety training course. The organiza- 
tion's safety functions were also analyzed in various team- 
building meetings. These resulted in specific changes, in- 
cluding the following: 

1. Reassignment of responsibility for the safety engineer- 
ing, and safety inspection and enforcement. 

2. Upgrading the mine safety person position from shift 
boss to foreman rank. 

3. Commitment to give safety training to each new 
supervisor. 

4. Commitment to develop a year-long schedule of safety 
incentive programs at the Lucky Friday Mine. 



Supervisory Skills Training 

This aspect of training was given a high priority from 
the outset. The most critical areas for training were con- 
sidered to be in company policies, record-keeping practices, 
standard production methods, and supervisory and leader- 
ship skills. Part of this instruction was handled by a com- 
mercially produced management training package. Other 
needed skills were taught by Hecla staff members. 



134 



Results 

In terms of productivity (average tons per worker-shift) 
and assay values of the silver and lead (a measure of the 
amount of waste rock extracted), the results were mixed, 
at best, and not very impressive. From the start of the OD 
intervention until the 9-week strike, productivity and assay 
values were dropping at Lucky Friday. After the strike, both 
improved. One would be hard pressed, however, to attribute 
this to the OD intervention. Figure 10-2 shows these results 
using the 1979 preintervention period as a baseline of 100%. 

With regard to safety, the results were more clear cut 
and dramatic, as shown in figure 10-3. As can be seen, the 
incidence rate of lost-time injuries was reduced by 46%, 
decreasing from 21.1 injuries per 200,000 employee-hours 
of exposure in 1980 to 11.4 injuries per 200,000 employee- 
hours in 1981. In 1982, that rate was reduced even further 
(to 4.0 for the month of January). The improvement in lost- 
time injuries from 1980 to 1981 was the equivalent of 540 
worker-shifts at the Lucky Friday. During this same time, 
the accident rate at neither the Star Mine nor the other 
district mines changed appreciably, although they did show 
some signs of decreasing early in 1982. These results 
strongly suggest that the OD intervention had a significant 
effect on safety at the Lucky Friday Mine. Thus, the efforts 
to reduce accidents appear to have been quite successful. 
Mine Safety and Health Administration (MSHA) officials 
responsible for the Idaho district expressed the belief that 
the personnel at the Lucky Friday Mine were making ex- 
ceptional progress toward improving their safety record. 

Cost 

The cost of the OD intervention project at Lucky Fri- 
day Mine was approximately $200,000— not including the 
time put into the meetings by Hecla management and 
workers. Hecla has trained in-house consultants for con- 
tinued OD interventions at its mines. 

Texasgulf Management Training Study 

The Texasgulf management training study was part of 
the same Bureau contract that supported the Hecla team- 
building project and is described in the same report by 
Fiedler (4). Although most practitioners of OD would argue 
that the intervention at Texasgulf was not really OD but 
was more along the lines of traditional management train- 
ing, the project is reviewed here rather than in chapter 9. 
because it makes an interesting comparison with the in- 
tensive OD-type intervention carried out at Rushton and 
Hecla. 

Background 

The target site for the management training program 
was a trona mine owned by Texasgulf and located near 
Granger, WY. The mine employed about 500 workers, half 
underground and half surface in the processing mill. Train- 
ing was conducted for managers and supervisors of both 
groups, starting in 1979. As was the case with the Hecla 
project, Murphy's law prevailed. In 1980, the mine began 
an effort to double its output. As a result, only 2 of the 15 
key managers retained the same job they held at the begin- 
ning of the study. 

The intervention began with a series of interviews to 
(a) familiarize the consultants with the organization, (b) 



120 




80 



70 



j-i 1 1 1 i i i 

Intervention » 



5 
■ 




KEY 

Productivity 
Silver assay 
Lead assay 




1979 



980 



981 



1982 



Figure 10-2.— Results of organizational development interven- 
tion at Lucky Friday Mine, showing productivity and assay values 
of silver and lead as a percentage of 1979 baseline, preinterven- 
tion period. 



30 



-Baseline 



Intervention 




o 
o 




key 

□ Lucky Friday Mine 
o Star Mine 
A District mines 



1 978 



1 979 



1 980 



I98I 



I982 



Figure 10-3.— Incident rates of lost-time accidents for the Lucky 
Friday Mine, Star Mine, and other mines in the Coeur d'Alene 
mining district. 



identify the major goals of management and supervisors, 
and (c) develop a list of critical behaviors to construct a per- 
formance evaluation scale for assessing the effects of the 
intervention. The training program itself consisted of the 
following four basic elements. 

Objective Supervisory Performance Appraisal 

A performance appraisal system was designed so that 
managers and supervisors could become aware of their own 
strengths and weaknesses, and those of their subordinates. 



135 



The rating scales concentrated on supervisory behaviors- 
how the supervisor acts, and how he or she can change in- 
effective behaviors. This type of performance evaluation has 
been found effective by other industries in motivating 
employees to improve their behavior at work. 

Leadership Training 

The intervention used the leader match program 
developed by Fiedler (6). This program is based on a gen- 
erally accepted view in the leadership area that the 
performance of leaders or managers depends both on their 
personalities and on the specific situations in which they 
operate. The method further assumes that it is generally 
much easier to change critical components of the leader- 
ship situation than one's personality or deeply ingrained 
habits of interpersonal interactions with subordinates. 

Leader match teaches individuals to diagnose their own 
leadership styles, as well as to diagnose the leadership situa- 
tions. The leaders are given detailed instruction on various 
methods for modifying the situations to match their par- 
ticular management approaches and personalities. The in- 
struction is provided by a trainer who uses a detailed 
manual, aided by videotaped illustrations, slides, and/or 
transparencies. 

This approach has been used by the U.S. Office of Per- 
sonnel Management and the military services, as well as 
by many organizations in the private sector. Validation of 
this method is described by Fiedler (5). 

Supervisory Skills Training 

This training method used videotaped vignettes in ac- 
tual and staged settings that taught the supervisor how to 
deal with specific problems with employees. The problems 
addressed included reinforcing safe behavior, correcting an 
employee, overcoming resistance to change, handling an 
irate employee, and creating a cooperative work team. 

Institutionalization 

Finally, to assure that the training would actually be 
used and would remain a permanent part of the organiza- 
tion, key personnel in the Texasgulf training department 
learned to administer the training methods. 

Results 

Productivity (tons per worker-hour) changed in the 
positive direction during the intervention. On average, the 
Texasgulf Mine increased productivity by 1.7% during the 
period of the intervention, whereas in the industry as a 
whole, productivity decreased by 2.9% during this period. 
The accident rate also improved during the last year of the 
intervention, while the average for the industry remained 
relatively constant. 

The Texasgulf Co. commissioned an independent man- 
agement consulting firm to conduct a company-wide job 
satisfaction and attitude survey in 1979, prior to the begin- 
ning of the intervention, and again in May of 1981, 4 
months after the intervention had ended. Of particular in- 
terest in this survey are the data relating to employee sat- 
isfaction and dissatisfaction with the mine's safety efforts. 
The comparison of the ratings of satisfaction prior and again 
shortly after the intervention showed satisfaction decreased 
only among administrative personnel and warehouse 



workers who were not the focus of the management train- 
ing program. Satisfaction increased most dramatically, by 
23%, among the underground mine personnel, and 19% 
among mill personnel, both of whom were involved in the 
intervention. 

Cost 

The development of the management training program 
and conduct of the study cost approximately $100,000, with 
most of the money being spent on development of the video- 
taped training modules and training manuals. This does 
not include the training of the mine managers and super- 
visors who attended all training sessions. Fiedler (4) con- 
cluded that the management training program was far less 
costly, and apparently no less effective in terms of the 
criteria evaluated than was the more intensive OD inter- 
vention carried out at Hecla's Lucky Friday Mine. 

Quality Control Circles 

In the last decade or so, there has been a steady and 
dramatic growth of quality control (QC) circles in the United 
States. QC circles are considered to be a Japanese manage- 
ment innovation, but actually the original ideas underlying 
the concept were introduced by U.S. experts in postwar 
Japan. A brief review of some of the characteristics and 
assumptions of QC circles follows, based on Goodman (8-9). 

A QC circle is a group of up to about 10 workers who 
voluntarily participate in improving a variety of perfor- 
mance indicators (e.g., quality, downtime, scrap, or rejects). 
The team meets on company time, and the foreman or a 
designated senior worker acts as the team leader. Train- 
ing is an important part of QC circles; time must be allo- 
cated to teaching workers both elementary problem-solving 
techniques and certain statistical data collection methods. 
Most organizations that use QC's have a QC facilitator who 
works with several circles in a given plant. Often a human 
resources staff person, the facilitator has received special 
training in working with groups. The facilitator's job is to 
provide support and followup activities to insure that the 
circle remains viable. While the circle leader runs the cir- 
cle meetings, the facilitator helps the group when special 
problems arise, interfaces with other groups in the organiza- 
tion, and provides assistance to the team leader. 

Several basic assumptions underlying the idea of quality 
circles follow. 

1. Joint problem solving should be a continuous process. 

2. Problem-solving activities should improve quality, 
costs, productivity, and safety. 

3. QC circle involvement should increase the technical 
and leadership skills of the work force. 

4. Change should be more enthusiastically accepted be- 
cause the workers will have been directly involved in pro- 
posing improvements. 

5. Recognition and participation in the problem-solving 
process should be desirable to workers. 

The benefits expected from the institution of QC circles 
include the following. 

1. For the worker, QC circles should provide a clear op- 
portunity to participate, to become involved in work, and 
to work with management. The circles should also provide 
powerful mechanisms for training workers in a variety of 
problem-solving, leadership, group-process, and presenta- 
tion skills. In addition, QC circles should be designed to pro- 
vide recognition for the workers. 



136 



2. For the company, the benefits should be in increased 
quality, lower downtime, greater organizational loyalty, and 
the availability of the resources of all employees for solv- 
ing problems. 

3. The current state of knowledge of QC circles should 
make introducing them relatively easy. 

QC circles are not without costs, or disadvantages, in- 
cluding the following. 

1. For foremen, QC circles can just mean more work 
placed on them by the company. Unless a foreman sees the 
QC circle as beneficial to his or her work, the circle will 
not be successful. As with some of the other OD changes, 
the circle could increase the workload and stress on the first- 
line supervisor. Some of this stress will be transferred to 
other levels of management. 

2. Most companies with QC circles use support person- 
nel or QC facilitators. These individuals must receive 
special training, which represents an additional cost of run- 
ning the program. 

3. Time is lost when workers meet; however, organiza- 
tions using the plan find no drop in productivity because 
of the motivational influence the circle meetings seem to 
have. 

QC Circles at the Captain Mine 

The QC circle program at the Arch Mineral Corp. South- 
western Illinois Coal Corp. Captain Mine, a surface coal 
mine located near Percy, IL, was described by Chironis (2). 
This program included a steering committee that set the 
overall goals for the circles and monitored the program. The 
steering committee consisted of four department heads, two 
employees (union), and a facilitator who was individually 
responsible for coordinating and directing the circles and 
for training the circle leaders. Specifically excluded from 
QC circle discussions were the topics of benefits and salaries, 
employment policies, discharge policies, and grievances and 
work rules. The circles were to concentrate on improving 
teamwork, company communications, and morale. 

An ideal group size for a QC circle is five to eight. At 
the Captain Mine, 22 people volunteered to be in the cir- 
cle; 7 were selected by drawing lots. Meetings were held 
approximately once a week, with each meeting lasting 
about 1 h. A project or problem was picked by the members 
of the circle, and the leader advised management of the 
selection. Typically, a number of problems were identified 
and listed by the circle. A partial list of problems identified 
by the QC circle of the Captain Mine included the following. 

Excessive downtime because of truck failures. 

Excess spillage off end of stacker. 

Tendency for some jobs to be started but not finished. 

Lack of walkways between new plant and breaker 
building. 

Lack of sufficient number of tractors. 

Tendency for some chutes to plug up. 

Insufficient housekeeping. 

Insufficient orientation of new tipple employees. 

Frequent misplacement of tools. 

Insufficient organization of tipple supply yard. 
Problem analysis is performed by the circles, with the 
assistance of appropriate technical experts as needed. The 
circle makes its recommendations directly to management 



by using a formal management-presentation procedure. 
This assures that management is fully cognizant of the prob- 
lem selection, analysis, and recommended solution. 



Results 

QC circles have not been extensively used in the min- 
ing industry, so that reports of results are not available. 
Even in industries where QC circles are widespread, little 
good data are available about their effectiveness. The Cap- 
tain Mine did report several innovative solutions to prob- 
lems identified, and a generally positive attitude toward 
the program by both management and workers. Several ad- 
ditional circles were formed at the Captain Mine. 



DISCUSSION 

The importance of motivation for safe and productive 
work habits is known by everyone in the mining industry. 
The link between organizational climate and safety and pro- 
ductivity is becoming more apparent. Organizational devel- 
opment as a means of positively altering the climate of an 
organization has just started to make inroads into the min- 
ing industry— and then only with large mining companies. 
The years ahead should see increased use of team-building 
and quality circle techniques, with more emphasis on 
middle-sized companies. 



REFERENCES 

1. Bell, C, M. Chemers, and F. Fiedler. Organizational Develop- 
ment Methods for Increasing Mine Safety. Paper in Mine Safety 
Education and Training, Seminar Proceedings: Bureau of Mines 
Technology Transfer Seminars, Pittsburgh, Pa., Dec. 9, 1980; 
Springfield, 111., Dec. 12, 1980; and Reno, Nev., Dec. 16, 1980: comp. 
by Staff. Pittsburgh Research Center. BuMines IC 8858. 1981. pp. 
71-76. 

2. Chironis, N. Quality Circles Raise Efficiency. Coal Age. Jan. 
1983, pp. 80-85. 

3. Coal Age. Rushton "Quality of Work" Experiment: Mixed 
Results. Jan. 1980, pp. 19-21. 

4. Fiedler, F.E., C.H. Bell, Jr., M.M. Chemers, and D. Patrick. 
The Effectiveness of Organizations and Management Training on 
Safety and Productivity in Metal/Non-Metal Underground Mining 
(contract J0387230. Perceptronics Inc.). BuMines OFR 191-84. 1983. 
296 pp.; NTIS PB 85-163285. 

5. Fiedler. F., and L. Mahar. A Field Experiment Validating Con- 
tingency Model Training. J. Appl. Psych., v. 64, 1979. pp. 247-254. 

6. Fiedler, F.. L. Mahar, and M. Chemers. Leader Match IV. Pro- 
grammed Instruction in Leadership for the U.S. Army. Dep. Psych.. 
Univ. of WA. Seattle, WA, 1977, 241 pp. 

7. Goodman, P. Assessing Organizational Change: The Rushton 
Quality of Work Experiment. Wiley. 1979. 391 pp. 

8. Goodman. P.. and R. Atkin. Labor-Management Problem Solv- 
ing Groups. Carnegie-Mellon Univ., Pittsburgh. PA. 1982. 11 pp. 

9. . New Concepts on Organizational Development. Paper 

in Ergonomics— Human Factors in Mining. Proceedings: Bureau 
of Mines Technology Transfer Seminars. Pittsburgh. Pa., December 
3, 1981; St. Louis, Mo.. December 10. 1981: and Denver. Colo.. 
December 15, 1981; comp. by Staff, Pittsburgh Research Center. 
BuMines IC 8866, 1981, pp." 84-97. 



137 



10. Lawler, E. Motivation in Work Organizations. Brooks and 
Cole, 1973, 267 pp. 

11. Maslow, A. Motivation and Personality. Harper and Row, 
1954, 348 pp. 

12 . Motivation and Personality. Harper and Row, 2d ed., 

1970, 382 pp. 

13. A Theory of Human Motivation. Psych. Rev., v. 50, 

1943, pp. 370-396. 

14. Mills, T. Altering the Social Structure in Coal Mining: A Case 
Study. Monthly Labor Rev., Oct. 1976, pp. 3-10. 



15. Sanders, M.S., T.V. Patterson, and J.M. Peay. The Effect of 
Organizational Climate and Policy on Coal Mine Safety (contract 
H0242039, U.S. Dep. Navy). BuMines OFR 108-77, 1976, 180 pp.; 
NTIS PB 267 781. 

16. Vroom, V. Work and Motivation. Wiley, 1964, 344 pp. 

17. Wood, R. Safety and Productivity in Numbers. Coal Age, Sept. 
1976, pp. 120-122. 

18. Zohar, D. Safety Climate in Industrial Organizations: 
Theoretical and Applied Implications. J. Appl. Psych., v. 65, 1980, 
pp. 96-102. 



138 



APPENDIX A.— STATIC ANTHROPOMETRIC DATA 
FOR MALE AND FEMALE MILITARY PERSONNEL' 





Figure A-1.— Standing body dimensions. 



Table A-1.— Standing body dimensions, inches 



Figure 




5th percentile 


95th percentile 


refer- 
ence 


122.4- 
lb male 


102.3-lb 
female 


201.9- 
Ib male 


164.3-lb 
female 


1 . . 
? 




Stature 

Eye height 


64.1 
59.5 
52.6 
46.4 
39.8 
24.4 
38.0 
30.0 
28.8 
18.7 
12.2 
28.6 
33.2 


60.0 
55.5 
48.4 
43.0 
37.4 
22.2 
36.6 
26.8 
26.2 
17.2 
11.4 
25.2 
289 


73.1 
682 
60.7 
53.7 
46.4 
29.2 
45.3 
36.1 
34.5 
23.1 
16.0 
35.8 
39.8 


68.5 
63.9 


3.. 
4.. 

5. . 

6. . 

7 


Shoulder (acromiale) height. . . 

Chest (nipple height) 1 

Elbow (radiale) height 

Fingertip (dactylion) height . . . 
Waist height 


56.6 
50.3 
43.6 
27.0 
43.4 


a 


Crotch height 


33.0 


9.. 
10 


Gluteal furrow height 

Kneecap height 


31.9 
20.7 


11 


Calf height . . . 


14.4 


1? 


Functional reach 


31.7 


13. 


Functional reach, extended . . . 


36.5 



Bustpoint height for women. 



1 From U.S. Department of Defense MIL-STD-1472B. "Human Engineering Guide to Equipment Design." Dec. 31. 1974. 



139 




15 |7 




rThr.zs 



19 20 



1 13 




Figure A-2.— Seated body dimensions. 



Table A-2.— Seated body dimensions, inches 



Figure 




5th percentile 


95th percentile 


refer- 
ence 


122.4- 
Ib male 


102.3-lb 
female 


201.9- 
Ib male 


164.3-lb 
female 


14.. 
15.. 
16.. 
17.. 
18.. 
19 




Vertical arm reach, sitting .... 

Sitting height, erect 

Sitting height, relaxed 

Eye height, sitting erect 

Eye height, sitting relaxed 

Midshoulder height 


50.6 
32.9 
32.1 
28.3 
27.6 
22.3 
21.3 
13.1 
12.5 
17.3 
6.9 
NA 
19.6 
15.6 
21.6 
17.9 
17.9 
43.5 


46.2 
31.1 
30.5 
26.6 
26.1 
21.2 
19.6 
12.1 
11.6 
15.7 
6.4 
4.1 
18.5 
15.0 
20.9 
17.1 
17.1 
39.2 


58.2 
38.2 
37.3 
33.3 
32.5 
26.7 
25.7 
15.8 
15.1 
20.5 
11.0 
NA 
23.7 
19.7 
25.9 
21.5 
21.5 
50.3 


54.9 
35.8 
35.3 
31.2 
30.7 
24.6 


20.. 
21.. 
7? 


Shoulder height, sitting 

Shoulder-elbow length 

Elbow-grip length 


23.7 
14.4 
14.0 


23.. 
?4 


Elbow-fingertip length 

Elbow rest height 


18.7 
10.6 


25.. 
26.. 
?7 


Thigh clearance height 

Knee height, sitting 

Popliteal height 


6.9 
21.8 
18.0 


28.. 
29.. 
30 


Buttock-knee length 

Buttock-popliteal length 

Buttock-heel length 


24.9 
20.7 
20.7 


31 


Functional leg length 


46.7 



NA Not available. 



140 



.33 





Figure A-3.— Body depth and breadth dimensions. 



Table A-3.— Body depth and breadth dimensions, inches 



Figure 




5th percentile 


95th percentile 


refer- 
ence 


122.4- 
Ib male 


102.3-lb 
female 


201.9- 
Ib male 


164.3-lb 
female 


32. . 


Chest depth 1 . 


7.5 
NA 
10.8 
11.9 
16.3 
15.7 
12.1 
8.4 


7.7 

7.2 

9.9 

12.4 

15.0 

13.0 

13.0 

9.1 


10.5 
NA 
13.5 
14.5 
19.6 
21.1 
15.1 
10.5 


10.7 


33 




Buttock depth 


9.6 


M 


Chest breadth 


12 4 


35. . 
36.. 
37. . 
38.. 
39. . 


Hip breadth, standing 

Shoulder (bideltoid) breadth . . 

Forearm-forearm breadth 

Hip breadth, sitting 

Knee-knee breadth 


15.6 
18.0 
17.7 
17.3 

12.0 











NA Not available. 

' Bust depth for women 



141 



APPENDIX B.— TYPICAL JOINT MOBILITY DATA 
SHOWING 5th and 95th PERCENTILE MALE AND FEMALE LIMITS 





Male Female 

Percentile 5th 95th 5th 95th 

/ Ankle extension (A) 18° 58° 36° 64° 

Ankle flexion (B) 23° 47° 9° 29° 



2 Knee flexion 



129° 159° 121° 147° 





r 3 


Knee rotation 
Medial (A) 

Knee rotation 
Lateral (B) 


15° 55° 25° 63° 
23° 63° 40° 72° 










Percentile. 



Male Female 
5th 95th 5th 95th 



; 7 Forearm supination (A) 77° 149° 61° 117° 
Forearm pronation (B) 37° 117° 77° 127° 



8 Elbow flexion 



26° 159° 140° 163° 




9 Shoulder flexion (A) 168° 208° 151° 184° 
Shoulder extension (B) 38° 84° 25° 58° 



v& 




^ Hip flexion 



92° 134° 56° 104° 




10 Shoulder abduction (A) 33° 63° Unknown 
Shoulder abduction (B) 106° 162° Unknown 





Hip abduction (A) 
Hip abduction (B) 



33° 
11° 



73° 
51° 



Unknown 
Unknown 



Hip rotation, sitting 






Lateral (A) 


16° 45° 


40° 72' 


Medial (B) 


16° 46° 


25° 63 




*f // Shoulder rotation 

Lateral (A) 13° 55° 15° 52° 

Shoulder rotation 

Medial (B) 61° 133° 139° 181° 



Figure B-1. — Typical joint mobility data. (Copyright 1972 by John Wiley and Sons, and reprinted by permission) 



142 



APPENDIX C— EXAMPLES OF PICTORIAL SAFETY SIGNS RECOMMENDED 

FOR USE IN THE MINING INDUSTRY 



(DANGER) 



I Electrical Explosion Flammable 

Red border. 

White 
background 

White and 
red image 



( CAUTION ) 






Fall Slip Trip 

Black border 



Yellow . 
background 

Black image 



Entanglement Crush Poison 

Corrosion Hot surface Pinch point 

^ ^ ^ 



Cut or sever 



^ 



143 



( PROHIBITION ) 



No smoking No open flame Do not touch 

Red circle 




Black image 
white background 




® 



(EGRESS- LOCATION) 



Exit Directional arrow 

Green 
background 




Green image §| ^»_«* L. ^^ ^J White 

on 
white doorway 




(MANDATORY ACTION) 



Eye protection Hard hat Ear protection 






Safety gloves Safety shoes 

Blue background 



o 




White image 



144 



(SAFETY LOCATION INFORMATION) 



First aid 



Eyewash Safety shower 



Green 
background 



White image 






L_ White 
background 



Green image 



(FIRE EQUIPMENT LOCATION) 
Fire extinguisher Fire hose and reel 



Red 
background 

White image 





145 



APPENDIX D.— SUMMARY OF SELECTED DATA REGARDING 
DESIGN RECOMMENDATIONS FOR CONTROL DEVICES 



Device 



Displacement 


Resistance 


Min 


Max 


Min 


Max 


0.125 in 


15 in 


10 oz 


40 oz 


0.5 in 


NAp 


NAp 


NAp 


1 in 


NAp 


NAp 


NAp 


NAp 


2.5 in 


NAp 


NAp 


NAp 


4 in 


NAp 


NAp 


NAp 


NAp 


4 lb 


20 lb 


NAp 


NAp 


10 lb 


20 lb 


30° 


120° 


10 oz 


40 oz 


15° 


140° 


10 oz 


40 oz 


30° 


1 40° 


10 oz 


40 oz 


NAp 


NAp 


NAp 


4.5-6 in/oz 


NAp 


NAp 


2 lb 


5 lb 


NAp 


NAp 


5 lb 


10 1b 


NAp 


NAp 


2.5 lb 


8 lb 


NAp 


14 in 


NAp 


NAp 


NAp 


38 in 


NAp 


NAp 


NAp 


NAp 


12 oz 


32 oz 


NAp 


NAp 


2 lb 


20-100 lb 


NAp 


90°-120° 


5 lb 


"30 lb 


0.5 in 


NAp 


NAp 


NAp 


1 in 


NAp 


NAp 


NAp 


NAp 


2.5 in 


NAp 


10 1b 


NAp 


7 in 


NAp 


180 1b 


NAp 


NAp 


4 lb NAp 


NAp 


NAp 


10 lb 


NAp 



Hand pushbutton, 0.5-in min size: Fingertip operation 

Foot pushbutton, 0.5-in min size: 

Normal operation 

Wearing boots 

Ankle flexion only 

Leg movement 

Will not rest on control 

May rest on control 

Toggle switch, 0.125- to 1-in-diam control tip, 0.5- to 2-in-length lever arm 

Rotary selector switch, 1- to 3-in length, 0.5- to 1-in width, 0.5-in depth: 

Visual positioning 

Nonvisual positioning 

Knob, continuous adjustment, finger-thumb, 2 0.5- to 1-in depth, 0.375- to 4-in diam, 1.5- to 3-in hand- 
palm diam 

Crank, 2 0.5- to 4.5-in radius for light loads and 0.5- to 20-in radius for heavy loads: 

Rapid, steady turning: 

< 3- to 5-in radius 

5- to 8-in radius 

For precise settings 

Levers: 3 

Fore-aft (1 hand) 

Lateral (1 hand) 

Finger grasp, 0.5- to 3-in diam 

Hand grasp, 1 .5- to 3-in diam 

Handwheel, 2 7- to 21-in diam, 0.75- to 2-in rim thickness 

Pedal, 3.5-in length, 2-in width: 

Normal use 

Heavy boots 

Ankle flexion 

Leg movement 

Will not rest on control 

May rest on control 



NAp Not applicable. 

1 When special requirements demand large separations, max should be 90°. 

2 Displacement of knobs, cranks, and handwheels should be determined by desired control-display ratio. 

3 Length depends on situation, including mechanical advantage required. For long movements, longer levers are desirable (so that movement is more linear). 

4 For 2-handed operation, max resistance of handwheel can be up to 50 lb. 



Source: McCormick, E., and M. Sanders. Human Factors in Engineering and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 



146 



APPENDIX E.— SELECTED DATA ON ACCESS SPACE REQUIRED 
TO PERFORM MAINTENANCE TASKS 1 




r— ©- 




C. Width 



D. Width 

E. Height 



F. Height 

G. Length 



H. Height 
I. Length 



Dimensions, in 
Minimum Preferred 



A. Height 48 

B. Width 27 36 



26 



42 
55 



31 
59 



17 
112 



40 



48 



36 



20 





Dimensions, in 
Minimum Preferred 




J. Height for - - 

Inspection 1 8 

Using small 
tools, making 
minor adjust- 
ments 24 

Reasonable 

arm 

extension 32 

K. Length 76 



L. Crawl 
through pipe 
diam 25 



M. Shoulder 
width 

N. Height 



0. Square 
Round 



21 
15 



18 
22 



30 



24 

20 



22 
24 



1 From U.S. Army Missile Command MIL-HDBK-759A, "Military Standardization Handbook: Human Factors Engineering Design for Army Mat- 
erial," 1981. 



147 



Opening 
dimension 




Dimension, in 
A B 



4.3 4.7 



Task 



Using common screwdriver, 
with freedom to turn hand 
through 180°. 




5 1 45 Using pliers and similar 

tools. 




Using "T" handle wrench, 
5.3 6.1 with freedom to turn hand 

through 180°. 



ft£=t 



m 



10.6 7.9 



Using open-end wrench, with 
freedom to turn wrench 
through 60°. 




B 



4.7 6.1 



Using Allen- type wrench 
with freedom to turn 
wrench through 60°. 




3.5 3.5 Using test probe, etc. 



148 



Opening dimensions 



Dimensions, in 
A B 



Task 




4.3 



4.7 



Grasping small objects 
(up to 2 in or more 
wide) with one hand. 




W+1.8 



Grasping large objects 
(2 in or more wide) 
with one hand . 




W+3 



Grasping large objects 
with 2 hands, with 
hands extended 
through openings up 
to fingers . 




W + 6 



Grasping large objects 
with 2 hands, with 
arms extended 
through openings up 
to wrists . 




W+6 



Grasping large objects 
with 2 hands, with 
arms extended 
through openings up 
to elbows . 



Or sufficient to clear part if part is larger than 5 in 



149 



75 pet of depth of reach (B) 
plus 6 in 




Y/////A 



A. Both arms, 1 opening 





4.5 in diam 



5in diam 

Add (3 in) for winter clothing 
B. Arm to elbow C. Arm to shoulder 



2 in 





D. Empty (flat) 




4in 



E Empty (clenched) 

Add 075in 
for gloves 



4in C 



F. Holding small object 

1.5-in diam 
H. Push button access 




l.75in 
Clearance around object 
6. Holding larger object 




3.5-in diam 
i". 2 -finger twist 



150 



INDEX 



Page 

Ability 128 

Access space 146-149 

Accident causation: Theories of 38-40 

Accident data analysis 125 

Accident liability theory 38 

Accident proneness 38 

Accident reduction programs 119 

Accident reporting 40 

Accident scenario, reconstruction of 24 

Accidents: 

Age and 38 

Back injury 82 

Cab design and 66 

Control design and 55 

Cost of 42-44 

Definition of 36 

Fatigue and 39 

Gold mining 35-36, 38 

Handtools and 78 

Haulage 37 

Human error and 36-38 

Illumination and 101 

Job experience and 39 

Material handling 91 

Near miss 36 

Supervisors 37, 39 

Transport underground 37 

Visibility and 71 

Acclimatization: Heat stress and 113 

Accommodation 20 

Action research model 131 

Acuity, visual 21 

Adaption 20 

Adjust to stress theory 39 

Aerobic capacity 83-84 

Age: 

Accidents and ". 38 

Accommodation and 20 

Hearing and 23 

Strength and 29 

Alarms (see: Auditory displays) 
Alphanumeric characters: 

Size of 50-51 

Stroke width to height ratio 50 

Typography of 50-51 

Width-to-height ratio 50 

Anthropometric data 138-140 

Anthropometry 27-28 

Limitations of data 28 

Aptitude 128 

Arm reach envelopes 28-29 

Attention 25-26 

Auditory displays 51-54 

Autonomous work groups 132 

Backlash 59 

Biomechanics: Of lifting 91-93 

Body dimensions (see: Anthropometric data) 

Canopy design 7 

Cardiac output 83-84 

Carpal tunnel syndrome 79 

Character typography 50-51 

Check-reading 48-49 

Checklists 3 

Circadian rhythms 30-31 

Climate (see: Heat stress and cold stress) 

Closed-loop system 10 

Coding: Controls 56-59 



Page 

Cold stress 113-114 

Performance and 113-114 

Protection from 114 

Color coding 48 

Color contrast 100 

Column format 13 

Compatibility 60-61 

Computer aids for design 17-18 

Continuous movements 27 

Contrast 100 

Control-display compatibility 60-61 

Control-response ratio 59 

Controls: 

Accidents related to 55 

Arrangement of 61 

Backlash and 59 

Coding of 56-59 

Control-response ratio 59 

Deadspace and 59 

Design criteria 145 

Identification of 56-59 

Placement of 61-66 

Resistance in 59 

Spacing of 66-67 

Types of 55-56 

Crewstation analysis program (CAP) 17-18 

Deadspace 59 

Decisionmaking 24-25 

Disability glare factor 102 

Displays: 

Arrangement of 61 

Criteria for evaluating 45 

Placement of 61-66 

Visual versus auditory 46 

(see also: Information displays, and specific types) 

Displays, auditory (see: Auditory displays) 

Displays, olfactory (see: Olfactory displays) 

Displays, visual (see: Visual displays) 

Diurnal rhythms (see: Circadian rhythms) 

Doorway placement: Surface equipment 73, 77 

Drill, jackleg 3 

Ear 22 

Ear protection (see: Hearing protection) 

Effective temperature 110-111 

Egress: Surface equipment 72-74, 76-77 

Electromyography 83 

EMG 83 

Endurance 30-31 

Energy consumption 83 

Energy expenditure: 

Factors that affect 86 

For common mining tasks 86-88 

Grades of work and 86 

Recommended levels of B8-S9 

Equivalent sound level 103 

Ergonomics (see: Human factors) 

Eustachian tube 22 

Evaluation testing 18 

Expectancy 129-131 

Expectancy theory 129-131 

Experience: Accidents and 39 

Extinction 121 

Eye 20 

Fatigue: Accidents and 39 

Federal Coal Mine Health and Safetv Act 6 

Feedback 120-121 



151 



Page 

Females: Handtools and 79 

Field of vision: (see also: Visibility) 

Low-seam equipment 66, 68-70 

Underground equipment 71-72 

Foot reach envelopes 28-29 

Front-end loader controls 62 

Frostbite 113 

Functions, of humans in systems 11 

Glare 101-102 

Goals freedom alertness theory 40 

Gold mining accidents 35-36, 38 

Grip strength: Handle size and 79 

Handles 95 

Handling materials injuries 41 

Handtool design 78-80 

Accidents and 78 

Handtool injuries 41 

Harrison Pick machine 5 

Haulage accidents 37 

Haulage truck: 

Maintainance problems 77-78 

Controls 62 

Drivers 25 

Hazard recognition 35 

Hearing 22-23 

Discrimination 23 

Intensity 23 

Discrimination of tones 23 

Localization of sound 22-23 

Masking and 23 

Hearing loss 104 

Hearing protection 107-108 

Heat cramps 110 

Heat exhaustion 110 

Heat stress 109-113 

Acclimization program for 113 

Conditions in mining Ill 

Exposure standards 112 

Indexes of 110-111 

Performance and 111-112 

Physiological effects of 109-110 

Protection from 112-113 

Unsafe behavior and 112 

Heat stress index Ill 

Heat stroke 110 

Heat transfer 109-110 

Human engineering (see: Human factors) 

Human error 34-38 

Accidents and 36-38 

Classification of 35-36 

Definition of 34 

Types of 35-36 

Human factors: 

Definition of 2 

History in mining 4-7 

History of 4 

In metal-nonmetal mining 7 

In processing plants 7 

In surface mining 7 

Roadblocks to application 3 

Human-hardware-environment system 3 

Ice jackets 113 

Illuminance 100 

Illumination 99-102 

Accidents and 101 

Accommodation and 20 

Measurement of 99-100 

Performance and 100-101 

Requirements for 101-102 

Safety and 101 



Page 

Incentive programs 119 

Information: 

Continuous 55 

Discrete 55 

Information displays: Tasks performed with 45 

Inherently safe mining systems 7 

Injuries: Types of 41 

Injury statistics 40-42 

Comparisons to other countries 42 

Industry-wide comaprisons 40-41 

Inputs 11 

International word-spelling alphabet 53 

Job severity index 96 

Joint mobility data 141 

Ladders 73-77 

Leader match program 135 

Learning: Concepts of 120-121 

Letters (see: Alphanumeric characters) 
Lifting: 

Aids to 95 

Biomechanics of 91-93 

Energy expenditure and 86-88 

Posture and 93-94 

Recommended limits 94-95 

Reducing risks 95-97 

Techniques of 94 

Light (see: Illumination) 

Lights: Signal, warning 49-50 

Limit of resolution 10 

Link analysis 16 

Loading, hand 2 

Loading, mechanical 6 

Loudspeaker system 53-54 

Luminance 100 

Luminance ratio 102 

Luminous flux 100 

Luminous intensity 100 

Machinery injuries 41 

Magic number 7 plus or minus 2 24 

Maintainability, equipment 77-78 

Maintenance: 

Access space requirements 146-149 

Training for 117 

Manikins 16 

Mantrip trolley: Noise and 107 

Manual materials handling (see: Materials handling) 

Masking 23 

Materials handling 90-97 

Activities 90 

Reducing risk 95-97 

Materials, weights of 91 

Memory 23-24 

Mental workload 26 

Metabolism 109-110 

Method of loci 24 

Miners, characteristics of 19 

Mockups 16 

Motivation 128-131 

Definition of 128 

Performance and 128-129 

Theory of 129-131 

Movement accuracy 27 

Movement time 27 

Movements: 

Continuous 27 

Positioning 27 

Range of 28 

Repetitive 27 

Muscles 82-83 



152 



Page 

Needs: Hierarchy of 129 

Noise: 102-108 

Conditions in mining 103-104 

Control of 105-107 

Exposure standards 104 

Hearing loss from 104 

Hearing protection and 107-108 

Indexes of 103 

Measurement of 102-103 

Performance and 105 

Physiological effects of 104-105 

Nystagmus 100 

OBSAC 122-123 

Olfactory displays 54 

Olfactory sense 23 

Open-loop system 10 

Operational sequence diagrams 13-14 

Organizational climate 131 

Organizational development 131-136 

Outputs 11 

Oxygen debt 83-84 

Pedals: Placement of 62 

Percentiles 27 

Pointer design 48 

Positioning movements 27 

Powered haulage injuries 41 

Preferred octave speech interference level 53 

Punishment 121 

Purkinje shift 20 

Quality control circles 135-136 

Reach envelopes: 

Arm 28-29 

Foot 28-29 

Low-seam equipment 66, 68-70 

Reaction time -. 26 

Reflectance 100 

Repetitive movements 27 

Resistance 59 

Resonance 105, 108 

Rest, amount required 89-90 

Retina 20 

Retroreflective material 49 

Reward 121 

Roof bolter: Energy consumption 88 

Roof bolter controls 56, 59, 62 

Rotary drills: Noise and 106 

Rushton experiment 132 

Safety awareness programs 126-127 

Safety climate 131 

Safety programs: 

Characteristics of 119 

Management and 119 

Seating: Low-seam equipment 66, 68-70 

Selection: For lifting 96 

Shift work 32 

Shuttle car 34 

Training system 122-123 

Signs 20, 126-127 

Conceptual compatibility 60 

Pictorial 51, 142-144 

Size of letters 51 

Typography 50-51 

Simulation 122-123 

Slip and fall injuries 41 

Smell 23 

Sound localization 107 

Sound pressure level 103 



Page 

Sound-level meter scales 103 

Speech 52-53 

Hearing protection and 53 

Intelligibility of 52-53, 107 

Intensity of 52 

Noise effects on 53 

Spine 92-93 

Stairs 73-77 

Standardization 61-62 

Static effort 85 

Stench systems 23, 54 

Strength 29-31 

Strength testing 96 

Supervisor accidents 37, 39 

Systems: 

Boundary of 10 

Characteristics of 9-11 

Definition of 9 

Objectives 12 

Specifications 12 

Stages in design of 12-18 

Task analysis: 12-16 

Formats for presenting 13-15 

Methods for collecting 13 

Type of information collected 13 

Team building 132-134 

Temperature (see: Heat stress and cold stress) 

Timelines 13, 15 

Tool design (see: Handtool design) 

Track dozers: Noise control in 105 

Training 116-126, 

128, 130 

Cost in mining 116 

Effectiveness of 116-117 

Heat stress 112 

Leadership 135 

Management 134-135 

Materials handling 96-97 

Methods of 122-124 

Needs assessment 124-125 

On the job 123-124 

Physical fitness 97 

Practices in United States 118-119 

Requirements for 117-118 

Systems design 124-126 

Transient adaptation 102 

Transport accidents 37 

Trigger finger 79 

Trolley operators 25-26 

Troubleshooting 24 

Undercutting coal 4-5 

Valence 129-131 

Vehicle design 63-66 

Vibration: Hand-arm 79-80 

Vibration-induced white finger 79-80 

Vibration, whole body 108-109 

Control of 109 

Effects of 108 

Exposure standards 108-109 

Surface miner exposure 109 

Vicarious learning 121 

Vigilance 25 

Visibility: From haulage trucks 7, 71 

Vision 20-22 

Accommodation 20 

Adaption 20 

Detection of movement 21-22 

Field of vision 20-21 

Visual acuity 21 



153 



Page 

Visual angle 21 

Visual displays 46-51 

Color coding 48 

Design of pointer 48 

Numerical progress 48 

Scale markers 47 

Warning-signal lights 49-50 



Page 

Walsh-Healy noise criteria 104 

Wet-bulb globe temperature Ill 

Windchill index 113 

Work physiology 82-84 

Work-rest cycles 89-90 

Workstation design: 

Seated 63-66 

Standing 66-67 



U.S. GOVERNMENT PRINTING OFFICE: 1988 - 505-016/80,013 



INT.-BU.OF MINES,PGH. ,PA. 28696 



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